Add a RadTreeView and fill it with nodes so that a vertical scrollbar is shown.

The RadTreeView.TopNode property indicates that it is expected to return the RadTreeNode which visual node element is the first visible one in the current view. But it always return the first data node in RadTreeView no matter which node is currently visible at the top. This is because it consider the RadTreeNode.Visible property. 

Workaround:

            TreeNodeElement neFirstVisible = this.radTreeView1.TreeViewElement.ViewElement.Children[0] as TreeNodeElement;
            RadMessageBox.Show("TopNode = " + neFirstVisible.Data.Text);