The 5 is a hardcoded max_level (cf. http://ez.no/doc/ez_publish/technical_manual/3_6/reference/template_operators/miscellaneous/treemenu) You can try to insert
Sorry Thomas, but I don't understand ... If 5 is the max depth that should be explored from a parent node, why doest it return me <b>21</b> subfolders ??