public function navigation_tree(global_navigation $navigation, $expansionlimit, array $options = array()) {
        $navigation->add_class('navigation_node');
        $navigationattrs = array(
            'class' => 'block_tree list',
            'role' => 'tree',
            'data-ajax-loader' => 'block_navigation/nav_loader');
        $content = $this->navigation_node(array($navigation), $navigationattrs, $expansionlimit, $options);
        if (isset($navigation->id) && !is_numeric($navigation->id) && !empty($content)) {
            $content = $this->output->box($content, 'block_tree_box', $navigation->id);
        }
        return $content;
    }