Hey Jeff, yes, I use that technique quite often.
I've never really thought of it as a tree view but I suppose that's correct. Really, in my skins they're still in unordered lists / list items, I just skin them to appear fancy.
A typical design is like this:
Parent menu items
Services | About Us | Contact
(children of about us)
Company
Director Bios
Team
History
Careers
Etc
So what I typically do is duplicate the DNNStandard menu (in DNN6) and call it something like 'sidenav'. Then I add NodeSelector="+0" (in ascx) to the sidenav so it only shows the children of the parent.
To get the 3rd level pages to appear, you need to use CSS to display the third level items when the 2nd level parent is selected. For that, you will need to use ULXSLT.xslt (not ULTokens.txt). (Check this resource:
http://www.dotnetnuke.com/Resources/W...)
Anyway, start simple but just having all the pages show up in the sidebar. Then style the nested lists accordingly. If you want more functionality (like having the third level pages show up when the 2nd level parent is selected) then look into the ULXSLT.XSLT file.
HTH
Aaron