private static function _isCollapsed($level, $childCount)
    {
        if (static::$expand_all) {
            return false;
        }

        $cascade = static::$_cascade;

        if ($cascade == null) {
            $cascade = static::_config('display', 'cascade', array());
        }

        if (isset($cascade[$level])) {
            return $childCount >= $cascade[$level];
        }
        return true;
    }