public function start_lvl(&$output, $depth = 0, $args = [])
    {
        $GLOBALS['comment_depth'] = $depth + 1;

        switch ($args['style']) {
            case 'div':
                break;
            case 'ol':
                $output .= '<ol class="children list-unstyled">'.PHP_EOL;
                break;
            case 'ul':
            default:
                $output .= '<ul class="children list-unstyled">'.PHP_EOL;
                break;
        }
    }