[Zope] how to expand a branch using dtml-tree ?

[BonviciniJ at keops.net]

I would like to know if its possible to expand a specified branch of a tree,using the dtml-tree tags.

I use this tag to display the tree of my site:

<dtml-tree expr="Ebullition.pages" nowrap=true single=1  skip_unauthorized>
           <A HREF="<dtml-var absolute_url>"><dtml-var title_or_id></A>  
 </dtml-tree>

But I have a problem.I want the chosen branch to keep expanded when the user click on the link.
At the moment, when I click on a branch (expanded or not), the page is called buit the tree is initialised (all branches collapsed)

So I wonder if its possible to kepp the branch expanded (by adding a special line, or send via post the id of the branch and expand it on the next loading of the page).
I add that The tree is in the same page and I don't want to use frames

thanks a lot for your help, and scuse for the english