[Zope] dtml-tree with data from multiple tables

I'd like to generate a tree with data from different SQL tables depending on the tree level. In other words, the first level data comes from one table, second level comes from another. How can the branches_expr expression determine what the current tree level is? Can I pass a parameter to let me know the current level? I tried the following, but it didn't work... <dtml-tree id=name branches_expr="child_lookup(_['tree-level'])"> Thanks, Lance __________________________________________________ Do You Yahoo!? Yahoo! Photos -- now, 100 FREE prints! http://photos.yahoo.com