Limitation - Category depth

I'm used unction from the menublock module to trim menu sitemap for depth. Here it

function menu_tree_depth_trim(&$tree, $depth_limit) {
  // Prevent invalid input from returning a trimmed tree.
  if ($depth_limit < 1) { return; }

  // Examine each element at this level to find any possible children.
  foreach (array_keys($tree) AS $key) {
    if ($tree[$key]['below']) {
      if ($depth_limit > 1) {
        menu_tree_depth_trim($tree[$key]['below'], $depth_limit-1);
      }
      else {
        // Remove the children items.
        $tree[$key]['below'] = FALSE;
      }
    }
    if ($depth_limit == 1 && $tree[$key]['link']['has_children']) {
      // Turn off the menu styling that shows there were children.
      $tree[$key]['link']['has_children'] = FALSE;
      $tree[$key]['link']['leaf_has_children'] = TRUE;
    }
  }
}

@Negor: Where are you supposed to add this code to make it work?