You could capture the scroll event of one treeview and use it to set the scroll position of the other. The problem is that the scroll event of TreeView was not exposed (I don't know if it is now as I don't have VS here at the moment, but I suspect that nothing has changed).
The most recent solution I could find was this
Stack Overflow[
^] post - it's in C# but you should be able to work it out or use one of the free on-line C# to VB converters.
Alternatively use a shared
VScrollbar[
^] for both TreeViews, capture its movements and set the TreeView up accordingly
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