In the "Big Tree" tab of the HelloTreeTableView toy I can sometimes get the tree items to expand or collapse on just a click on the triangle, but then it gets into states where I have to double click on the triangle to do the same thing. The "Root" entry always seems to respond to just a regular click on its triangle, but the other items in the tree tend to mostly require a double-click.

The other tabs have tree items that all seem to reliably respond to just a regular click.