protected function fillXml(\SimpleXMLElement $element, $data)
    {
        foreach ($data as $key => $value) {
            if (is_array($value) || is_object($value)) {
                if (!is_numeric($key)) {
                    $child = $element->addChild($key);
                } else {
                    $child = $element;
                }
                
                $this->fillXml($child, $value);
            } else {
                $element->addChild($key, $value);
            }
        }
    }