Treeview dropdown datawindow

Hi.

I'm trying out the treeview datawindow and would like to have it inside a dropdown. I've made a small example with data from the demo database (see attached file).

Now, I would like to be able to show whatever node I clicked. The problem is I have to choose the display column as, in this example, either Department name or Employee name. How can I make the dropdown show whatever node I'm at?