handlers/views_handler_sort_menu_hierarchy.inc

<?php

class views_handler_sort_menu_hierarchy extends views_handler_sort {
  function query() {
    $this->ensure_my_table();
    $max_depth = isset($this->definition['max depth']) ? $this->definition['max depth'] : MENU_MAX_DEPTH;
    for ($i = 1; $i <= $max_depth; ++$i) {
      $this->query->add_orderby($this->table_alias, $this->field . $i, $this->options['order']);
    }
  }
}