sub menu() {
   my ($act_path, $select_path)=@_;
   my $out="<ul>";
   $out.=item($act_path);

   if ( display( $act_path, $select_path ) ) {
        $out.=menu( $_, $select_path ) for ( childs ($act_paths) );
   }
   $out.="</ul>";
   return $out;
}

$tree=menu("",$select_path);