无限极分类--递归法

 /**
     * 无限极分类
     * @param array $data 可迭代数组
     * @param int $pid 父级id
     * @return array
     */
    public static function getTree(array $data,$pid = 0): array
    {
        $tree = [];
        foreach ($data as &$item){
            if ($item['pid'] === $pid){
                $item['children'] = self::getTree($data,$item['id']);
                $tree[] = $item;
            }
        }
        return $tree;
    }