public static function getRootDomain($url)
    {
        $host = $domain = self::getHostname($url);
        $root = false;

        if (($dotsCount = substr_count($host, '.')) > 0) {
            $last = $domain;
            while ($dotsCount > -1) {
                if (self::isHostInSuffixList($domain)) {
                    $root = $last;
                    break;
                }
                $last = trim($domain, '.');
                $domain = substr($last, strpos($last, '.'));
                $dotsCount = $dotsCount - 1;
            }
        }

        return $root;
    }