This event is triggered before a tree node is expanded, by clicking on 'plus', in case the node has not been expanded before, it will instantly be filled with the files found in that particular path (by AddShellItem(ShellTreeNode))

protected override void OnBeforeExpand(
	TreeViewCancelEventArgs e
)

Protected Overrides Sub OnBeforeExpand ( _
	e As TreeViewCancelEventArgs _
)

protected:
virtual void OnBeforeExpand(
	TreeViewCancelEventArgs^ e
) override