This is a simple two-level treeview. Actually in D.H.E. you can make a thing like that only by using an HTML box. Maybe in the future I'll create something like that.
I know this can be done with Adobe's free Spry library and I believe Scriptaculous also. You can see one example that uses similar coding using the spry library here: http://greater-emmanuel.org Notice how you can expand and close the stories on the main page.