Clean up when node removed.

src/Avalonia.Controls/SelectionNode.cs

@@ -655,6 +655,7 @@ namespace Avalonia.Controls
                         if (_childrenNodes[index] != null)
                         {
                             RealizedChildrenNodeCount--;
+                            _childrenNodes[index]!.Dispose();
                         }
                         _childrenNodes.RemoveAt(index);
                     }

tests/Avalonia.Controls.UnitTests/SelectionModelTests.cs

@@ -964,6 +964,20 @@ namespace Avalonia.Controls.UnitTests
             }
         }
 
+        [Fact]
+        public void Removing_Item_Unhooks_CollectionChanged_Handlers()
+        {
+            var data = CreateNestedData(2, 2, 2);
+            var target = new SelectionModel { Source = data };
+
+            target.SelectAll();
+
+            var toRemove = (AvaloniaList<object>)data[1];
+            data.Remove(toRemove);
+
+            Assert.Equal(0, GetSubscriberCount(toRemove));
+        }
+
         [Fact]
         public void Should_Not_Treat_Strings_As_Nested_Selections()
         {