[Zope] Passing query strings in trees

All, I have a Zope tree structure that requires a query variable to be passed to it. The first time through, I can pass it on the http request with no problem: http://www.mgmt-inc.com/some_object?variable=value But this query string is not included in the [+] and [-] links to expand/contract the tree so that I can pass it on to the next rendering of this object. How do I do this? Thanks for the help, Jim