获取树结构(可游离数据(不从顶级节点获取))

$list = [
    ['id'=>'222', 'name'=>'李世民', 'parentid'=>'111'],
    ['id'=>'999', 'name'=>'李隆基', 'parentid'=>'777'],
    ['id'=>'111', 'name'=>'李渊', 'parentid'=>'0'],
    ['id'=>'555', 'name'=>'李治', 'parentid'=>'222'],
    ['id'=>'666', 'name'=>'李显', 'parentid'=>'555'],
    ['id'=>'777', 'name'=>'李旦', 'parentid'=>'555'],
    ['id'=>'444', 'name'=>'李建成', 'parentid'=>'111'],
    ['id'=>'333', 'name'=>'李元霸', 'parentid'=>'111'],
    ['id'=>'888', 'name'=>'李重茂', 'parentid'=>'666'],
];
$parentIds = [];
foreach ($list as $item){
    $key = $item['parentid'];
    $parentIds[$key][] = $item['id'];
}

$tree = createTreeData2($parentIds, $list);
print_r(json_encode($tree));die;
/**
 * 创建树数据
 */
function createTreeData2($parentIds, &$list)
{
    $res = [];
    if(!$list){
        return $res;
    }
    foreach ($parentIds as $parentId => $childIds){
        //先查找 当前父类id是否存在 上级
        $childrenNodes = array_filter($list, function ($item)use($parentId){
            return $item['id'] == $parentId;
        });
        //如果存在 (一个子类不可能同时拥有两个父类, 所以 $childrenNodes是 单个元素)
        if($childrenNodes){
            $childrenNodes =  array_shift($childrenNodes);
            // 再查找 这个父类 是否 存在父类
            $chs = array_filter($list, function ($item)use($parentId,$childrenNodes){
                return $item['id'] == $childrenNodes['parentid'];
            });
            //如果不存在, 那么他就是最顶级了 (如果存在呢?)
            if(!$chs){
                $child = makeNode2($childrenNodes, $list);
                if($child){
                    $childrenNodes['children'] = array_values($child);
                }
                array_push($res, $childrenNodes);
            }
        }else{
            foreach ($childIds as $k => $v){
                if(!isset($parentIds[$v])){
                    $tp = array_filter($list, function ($item)use($v){
                        return $item['id'] == $v;
                    });
                    $tp = array_shift($tp);
                    array_push($res, $tp);
                }
            }
        }
    }
    return $res;
}

/**
 * 构造单个节点
 */
function makeNode2($childrenNodes, &$list)
{
    $childrens = array_filter($list, function ($item)use ($childrenNodes)
    {
        return $item['parentid'] == $childrenNodes['id']; }
    );
    if($childrens){
        foreach ($childrens as $key => $children){
            $child  = makeNode2($children, $list);
            if($child){
//                    $child = array_shift($child);
                $childrens[$key]['children'] =  array_values($child);
            }
        }
    }
    return $childrens;
}