bookmap switch to document view

Adobe Framemaker Bookmap has an icon at the top of the bookmap to "Switch To Document View".   When you click on that button, it switches the bookmap to a document format.  The only problem is there is no button to take you back to the tree view.  I have had to shut the file down and re-open it in order to get my bookmap back.  Since the "Switch To Document View" is at the top of the tree, with other options, I have accidently pressed it several times.

I don't know why Framemaker creates these black holes in the user interface.  Can anyone tell me how you switch back to tree view after you go into the Document View?

Thanks!