Vertical scroll bar not fully displayed

[David]

When my tree view expands to no longer fit the window, vertical scroll bars do not appear. When I set:

ScrollViewer.VerticalScrollBarVisibility="Visible"

I initially get a disabled scroll bar. When I expand my tree, the height of the scroll bar is taller than the window so I still can't scroll.
My tree is inside a RadDocumentPane. I have a RadGridView in another RadDocumentPane and scrolling works for it.
Is there something special for a RadTreeView?

[David]

I fixed it by adding to the rad tree view:

MaxHeight="{Binding ActualHeight,ElementName=root}"

where "root" refers to my UserControl. (I misspoke before. My tree is in a UserControl, which is in a RadDocumentPane).