PHP processing tree and infinite processing

/**
     *  Merging of arrays , And plus html Identification prefix 
     * @param array $data
     * @param int $pid
     * @param string $html
     * @param int $level
     * @return array
     */
    public function treeLevel(array $data,  $pid = 0,  $html = '---', $level = 0) {
        static $arr = [];
        foreach ($data as $val) {
            if ($pid == $val['pid']) {
                //  How many times to repeat a character 
                $val['html'] = str_repeat($html, $level * 2);
                $val['level'] = $level + 1;
                $arr[] = $val;
                $this->treeLevel($data, $val['id'], $html, $val['level']);
            }
        }
        return $arr;
    }




/**
     *  Data Multilevel 
     * @param array $data
     * @param int $pid
     * @return array
     */
    public function subTree($data,  $pid = 0) {
        //  The result returned 
        $arr = [];
        foreach ($data as $val) {
            //  A given PID Is the superior of the current record ID
            if ($pid == $val['pid']) {
                //  recursive 
                $val['sub'] = $this->subTree($data,$val['id']);
                $arr[] = $val;
            }
        }
        return $arr;
    }