Yes, thanks ;) I aready see that, but it just list articles, and I really want a tree view...
For now, I take the experimental module mod_k2cats by Nilesh Toshniwal here :
community.getk2.org/forum/topics/expandable-menu-option-for-...
It don't work great with SEF url, but it's not a big problem for me :) It's not really a tree view, it's an accordion menu, but finally I prefer that instead of a tree view :)