Index: Core/Common/src/Core.Common.Controls.TreeView/TreeNodeInfo.cs
===================================================================
diff -u -r99b31025be8be46190cf15e58aec262a4bb18858 -r5d0ea46dea2c2d063c7fb5c58bed3be219be1c85
--- Core/Common/src/Core.Common.Controls.TreeView/TreeNodeInfo.cs	(.../TreeNodeInfo.cs)	(revision 99b31025be8be46190cf15e58aec262a4bb18858)
+++ Core/Common/src/Core.Common.Controls.TreeView/TreeNodeInfo.cs	(.../TreeNodeInfo.cs)	(revision 5d0ea46dea2c2d063c7fb5c58bed3be219be1c85)
@@ -117,9 +117,10 @@
 
         /// <summary>
         /// Gets or sets an action for obtaining the logic to perform after checking or unchecking the tree node.
-        /// The <see cref="TreeNode"/> parameter represents the tree node which is checked.
+        /// The first <see cref="object"/> parameter represents the data of the tree node.
+        /// The second <see cref="object"/> parameter represents the data of the parent tree node.
         /// </summary>
-        public Action<TreeNode> OnNodeChecked { get; set; }
+        public Action<object, object> OnNodeChecked { get; set; }
 
         /// <summary>
         /// Gets or sets a function for checking whether or not the tree node can be dragged to another location.
@@ -255,9 +256,10 @@
 
         /// <summary>
         /// Gets or sets an action for obtaining the logic to perform after checking or unchecking the tree node.
-        /// The <see cref="TreeNode"/> parameter represents the tree node which is checked.
+        /// The <see cref="TData"/> parameter represents the data of the tree node.
+        /// The <see cref="object"/> parameter represents the data of the parent tree node.
         /// </summary>
-        public Action<TreeNode> OnNodeChecked { get; set; }
+        public Action<TData, object> OnNodeChecked { get; set; }
 
         /// <summary>
         /// Gets or sets a function for checking whether or not the tree node can be dragged to another location.
@@ -337,8 +339,8 @@
                                 ? tag => treeNodeInfo.IsChecked((TData) tag)
                                 : (Func<object, bool>) null,
                 OnNodeChecked = treeNodeInfo.OnNodeChecked != null
-                                    ? sourceNode => treeNodeInfo.OnNodeChecked(sourceNode)
-                                    : (Action<TreeNode>) null,
+                                    ? (tag, parentTag) => treeNodeInfo.OnNodeChecked((TData) tag, parentTag)
+                                    : (Action<object, object>) null,
                 CanDrag = treeNodeInfo.CanDrag != null
                               ? (tag, sourceNode) => treeNodeInfo.CanDrag((TData) tag, sourceNode)
                               : (Func<object, TreeNode, DragOperations>) null,
Index: Core/Common/src/Core.Common.Controls.TreeView/TreeViewControl.cs
===================================================================
diff -u -r99b31025be8be46190cf15e58aec262a4bb18858 -r5d0ea46dea2c2d063c7fb5c58bed3be219be1c85
--- Core/Common/src/Core.Common.Controls.TreeView/TreeViewControl.cs	(.../TreeViewControl.cs)	(revision 99b31025be8be46190cf15e58aec262a4bb18858)
+++ Core/Common/src/Core.Common.Controls.TreeView/TreeViewControl.cs	(.../TreeViewControl.cs)	(revision 5d0ea46dea2c2d063c7fb5c58bed3be219be1c85)
@@ -550,7 +550,7 @@
             var treeNodeInfo = GetTreeNodeInfoForData(e.Node.Tag);
             if (treeNodeInfo.OnNodeChecked != null)
             {
-                treeNodeInfo.OnNodeChecked(e.Node);
+                treeNodeInfo.OnNodeChecked(e.Node.Tag, e.Node.Parent != null ? e.Node.Parent.Tag : null);
             }
         }
 
Index: Core/Plugins/src/Core.Plugins.OxyPlot/Legend/LegendView.cs
===================================================================
diff -u -rc68064014494505f833de7749ee7b3d879f723d6 -r5d0ea46dea2c2d063c7fb5c58bed3be219be1c85
--- Core/Plugins/src/Core.Plugins.OxyPlot/Legend/LegendView.cs	(.../LegendView.cs)	(revision c68064014494505f833de7749ee7b3d879f723d6)
+++ Core/Plugins/src/Core.Plugins.OxyPlot/Legend/LegendView.cs	(.../LegendView.cs)	(revision 5d0ea46dea2c2d063c7fb5c58bed3be219be1c85)
@@ -53,7 +53,7 @@
                 CanDrag = (pointData, sourceNode) => DragOperations.Move,
                 CanCheck = pointData => true,
                 IsChecked = pointData => pointData.IsVisible,
-                OnNodeChecked = PointBasedChartDataOnNodeChecked
+                OnNodeChecked = PointDataOnNodeChecked
             });
 
             treeViewControl.RegisterTreeNodeInfo(new TreeNodeInfo<LineData>
@@ -63,7 +63,7 @@
                 CanDrag = (lineData, sourceNode) => DragOperations.Move,
                 CanCheck = lineData => true,
                 IsChecked = lineData => lineData.IsVisible,
-                OnNodeChecked = PointBasedChartDataOnNodeChecked
+                OnNodeChecked = LineDataOnNodeChecked
             });
 
             treeViewControl.RegisterTreeNodeInfo(new TreeNodeInfo<AreaData>
@@ -73,7 +73,7 @@
                 CanDrag = (areaData, sourceNode) => DragOperations.Move,
                 CanCheck = areaData => true,
                 IsChecked = areaData => areaData.IsVisible,
-                OnNodeChecked = PointBasedChartDataOnNodeChecked
+                OnNodeChecked = AreaDataOnNodeChecked
             });
 
             treeViewControl.RegisterTreeNodeInfo(new TreeNodeInfo<ChartDataCollection>
@@ -106,19 +106,30 @@
 
         # region ChartData
 
-        private void PointBasedChartDataOnNodeChecked(TreeNode node)
+        private void PointDataOnNodeChecked(PointData pointData, object parentData)
         {
-            var pointBasedChartData = node.Tag as PointBasedChartData;
-            if (pointBasedChartData != null)
-            {
-                pointBasedChartData.IsVisible = node.Checked;
-                pointBasedChartData.NotifyObservers();
+            PointBasedChartDataOnNodeChecked(pointData, parentData);
+        }
 
-                var parentData = node.Parent != null ? node.Parent.Tag as IObservable : null;
-                if (parentData != null)
-                {
-                    parentData.NotifyObservers();
-                }
+        private void LineDataOnNodeChecked(LineData lineData, object parentData)
+        {
+            PointBasedChartDataOnNodeChecked(lineData, parentData);
+        }
+
+        private void AreaDataOnNodeChecked(AreaData areaData, object parentData)
+        {
+            PointBasedChartDataOnNodeChecked(areaData, parentData);
+        }
+
+        private void PointBasedChartDataOnNodeChecked(PointBasedChartData pointBasedChartData, object parentData)
+        {
+            pointBasedChartData.IsVisible = !pointBasedChartData.IsVisible;
+            pointBasedChartData.NotifyObservers();
+
+            var observableParent = parentData as IObservable;
+            if (observableParent != null)
+            {
+                observableParent.NotifyObservers();
             }
         }
 
Index: Core/Plugins/test/Core.Plugins.OxyPlot.Test/Legend/AreaDataTreeNodeInfoTest.cs
===================================================================
diff -u -rb3883ecc0719d5df114cacc849796c0ca420507d -r5d0ea46dea2c2d063c7fb5c58bed3be219be1c85
--- Core/Plugins/test/Core.Plugins.OxyPlot.Test/Legend/AreaDataTreeNodeInfoTest.cs	(.../AreaDataTreeNodeInfoTest.cs)	(revision b3883ecc0719d5df114cacc849796c0ca420507d)
+++ Core/Plugins/test/Core.Plugins.OxyPlot.Test/Legend/AreaDataTreeNodeInfoTest.cs	(.../AreaDataTreeNodeInfoTest.cs)	(revision 5d0ea46dea2c2d063c7fb5c58bed3be219be1c85)
@@ -145,18 +145,13 @@
         {
             // Setup
             var areaData = mocks.StrictMock<AreaData>(Enumerable.Empty<Tuple<double, double>>());
-            var areaDataTreeNode = new TreeNode
-            {
-                Tag = areaData
-            };
 
             mocks.ReplayAll();
 
             areaData.IsVisible = initialVisibleState;
-            areaDataTreeNode.Checked = !initialVisibleState;
 
             // Call
-            info.OnNodeChecked(areaDataTreeNode);
+            info.OnNodeChecked(areaData, null);
 
             // Assert
             Assert.AreEqual(!initialVisibleState, areaData.IsVisible);
@@ -171,25 +166,15 @@
             // Setup
             var observable = mocks.StrictMock<IObservable>();
             var areaData = mocks.StrictMock<AreaData>(Enumerable.Empty<Tuple<double, double>>());
-            var areaDataTreeNode = new TreeNode
-            {
-                Tag = areaData
-            };
-            var parentNode = new TreeNode
-            {
-                Tag = observable
-            };
 
             observable.Expect(o => o.NotifyObservers());
 
             mocks.ReplayAll();
 
             areaData.IsVisible = initialVisibleState;
-            parentNode.Nodes.Add(areaDataTreeNode);
-            areaDataTreeNode.Checked = !initialVisibleState;
 
             // Call
-            info.OnNodeChecked(areaDataTreeNode);
+            info.OnNodeChecked(areaData, observable);
 
             // Assert
             Assert.AreEqual(!initialVisibleState, areaData.IsVisible);
Index: Core/Plugins/test/Core.Plugins.OxyPlot.Test/Legend/LineDataTreeNodeInfoTest.cs
===================================================================
diff -u -r96fff35cedc43c8be2da620efa3d1b9cb3e42238 -r5d0ea46dea2c2d063c7fb5c58bed3be219be1c85
--- Core/Plugins/test/Core.Plugins.OxyPlot.Test/Legend/LineDataTreeNodeInfoTest.cs	(.../LineDataTreeNodeInfoTest.cs)	(revision 96fff35cedc43c8be2da620efa3d1b9cb3e42238)
+++ Core/Plugins/test/Core.Plugins.OxyPlot.Test/Legend/LineDataTreeNodeInfoTest.cs	(.../LineDataTreeNodeInfoTest.cs)	(revision 5d0ea46dea2c2d063c7fb5c58bed3be219be1c85)
@@ -145,18 +145,13 @@
         {
             // Setup
             var lineData = mocks.StrictMock<LineData>(Enumerable.Empty<Tuple<double, double>>());
-            var lineDataTreeNode = new TreeNode
-            {
-                Tag = lineData
-            };
 
             mocks.ReplayAll();
 
             lineData.IsVisible = initialVisibleState;
-            lineDataTreeNode.Checked = !initialVisibleState;
 
             // Call
-            info.OnNodeChecked(lineDataTreeNode);
+            info.OnNodeChecked(lineData, null);
 
             // Assert
             Assert.AreEqual(!initialVisibleState, lineData.IsVisible);
@@ -171,25 +166,15 @@
             // Setup
             var observable = mocks.StrictMock<IObservable>();
             var lineData = mocks.StrictMock<LineData>(Enumerable.Empty<Tuple<double, double>>());
-            var lineDataTreeNode = new TreeNode
-            {
-                Tag = lineData
-            };
-            var parentNode = new TreeNode
-            {
-                Tag = observable
-            };
 
             observable.Expect(o => o.NotifyObservers());
 
             mocks.ReplayAll();
 
             lineData.IsVisible = initialVisibleState;
-            parentNode.Nodes.Add(lineDataTreeNode);
-            lineDataTreeNode.Checked = !initialVisibleState;
 
             // Call
-            info.OnNodeChecked(lineDataTreeNode);
+            info.OnNodeChecked(lineData, observable);
 
             // Assert
             Assert.AreEqual(!initialVisibleState, lineData.IsVisible);
Index: Core/Plugins/test/Core.Plugins.OxyPlot.Test/Legend/PointDataTreeNodeInfoTest.cs
===================================================================
diff -u -rb3883ecc0719d5df114cacc849796c0ca420507d -r5d0ea46dea2c2d063c7fb5c58bed3be219be1c85
--- Core/Plugins/test/Core.Plugins.OxyPlot.Test/Legend/PointDataTreeNodeInfoTest.cs	(.../PointDataTreeNodeInfoTest.cs)	(revision b3883ecc0719d5df114cacc849796c0ca420507d)
+++ Core/Plugins/test/Core.Plugins.OxyPlot.Test/Legend/PointDataTreeNodeInfoTest.cs	(.../PointDataTreeNodeInfoTest.cs)	(revision 5d0ea46dea2c2d063c7fb5c58bed3be219be1c85)
@@ -145,18 +145,13 @@
         {
             // Setup
             var pointData = mocks.StrictMock<PointData>(Enumerable.Empty<Tuple<double, double>>());
-            var pointDataTreeNode = new TreeNode
-            {
-                Tag = pointData
-            };
 
             mocks.ReplayAll();
 
             pointData.IsVisible = initialVisibleState;
-            pointDataTreeNode.Checked = !initialVisibleState;
 
             // Call
-            info.OnNodeChecked(pointDataTreeNode);
+            info.OnNodeChecked(pointData, null);
 
             // Assert
             Assert.AreEqual(!initialVisibleState, pointData.IsVisible);
@@ -171,25 +166,15 @@
             // Setup
             var observable = mocks.StrictMock<IObservable>();
             var pointData = mocks.StrictMock<PointData>(Enumerable.Empty<Tuple<double, double>>());
-            var pointDataTreeNode = new TreeNode
-            {
-                Tag = pointData
-            };
-            var parentNode = new TreeNode
-            {
-                Tag = observable
-            };
 
             observable.Expect(o => o.NotifyObservers());
 
             mocks.ReplayAll();
 
             pointData.IsVisible = initialVisibleState;
-            parentNode.Nodes.Add(pointDataTreeNode);
-            pointDataTreeNode.Checked = !initialVisibleState;
 
             // Call
-            info.OnNodeChecked(pointDataTreeNode);
+            info.OnNodeChecked(pointData, observable);
 
             // Assert
             Assert.AreEqual(!initialVisibleState, pointData.IsVisible);