wp_list_pages – tree with collapsed subpages

Hello all,
I am able to list, say, 2 levels of pages – e.g. wp_list_pages(‘echo=0&depth=2&title_li=’);

Every page at depth 2 contains plenty of subpages. => entire menu generated by wp_list_pages is too huge.
Is it possible to generated 3rd level subpages menu when the users clicks on a 2nd level page?
Something like a collapsable product tree.

Example:
Products
-SW
+-Sub1
+-Page1
+-Page2
+-Sub2
-HW
+-Sub3
+-Sub4

I would like to have a menu where Page1 and Page2 are shown only if the user browses Sub1 page or any of its subpages (ie. Page1 or Page2)

Is it possible to to that?
Thanks in advance,
meereck