Consider
MyTreeView.Select()
Reason:
When a button is clicked, the TreeView loss focus since the user clicked elsewhere.
When the treeview is not in focus, the highlighted item is not seen.
It can be mistaken as no item is selected, or "the selected node is lost".
Putting the TreeView back in focus restores the highlight.
This can be done in the button's click event handler.
So after clicking the button, the focus to the treeview is restored programatically.