1. Have some tree with nodes and subnodes. Expand some of the nodes one by one until vertical scrollbar appears.
At the same time, there should be more nodes which have subnodes left
2. Do "Expand all" on some other node which is not expanded yet. Code used: "node.ExpandAll()"
Scroll bar reflect the area change and you can scroll up and down, it's ok
3. Do "Collapse all" on same node. Code used: "node.Collapse()"