[Zope] dtml-tree recursion

Hi there ! I trying to work with dtml-tree tag to show my site contents. I have a dtml-method that does that. Still, the calling Dtml Document passes to the method that shows the tree, a variable (kind of a parameter) that i need to access in the method. All goes OK : ) both the tree and the variable are displayed ! The problem is when i click the +/- icon Zope gives me an error that couldn't access the variable passed as argument. I think that it might be a problem with recursion of the tree. does anyone have an ideia how to solve this recursion problem ? thanks in advance and best regards, Nuno