Scrollbar not appearing when tree extends beyond bottom of screen

Vaadin 6 / 7 / 8
1

Here is the layout:

VerticalLayout with View
VerticalLayout
TabSheet with 4 tabs
problem tab is a VerticalLayout
Horizontal Layout
Button
Panel
VerticalLayout
Tree

Button(Logout)

When the tree extends beyond the bottom I can see tree items though the logout button at the bottom - but no scroll bar.

I’m not sure where I should be putting the various sizeFull or sizeUndefined.

Vaadin 7.6.4