递归实现

function   ad(){
     $res=db::table("category")->get();
   $res= json_encode($res);
    $res= json_decode($res,1);
    $arr= $this->gettree($res,0);
      var_dump($arr);
}

 function  gettree($data,$pid){
     $tree=[];
     foreach ($data as $k=>$v){
         if ($v['pid']==$pid){
             $v['son']=$this->gettree($data,$v['id']);
             $tree[]=$v;
         }
     }
     return $tree;

 }