<?php
$ori=json_decode(<<<JSON
[{"category":"ABC","orderID":"12345","Name":"Pen","Name2":"Black"},
{"category":"ABC","orderID":"34545","Name":"Pencil","Name2":"White"},
{"category":"ABC","orderID":"34545","Name":"Pen","Name2":"Black"},
{"category":"DEF","orderID":"12345","Name":"Pencil","Name2":"Black"},
{"category":"DEF","orderID":"12345","Name":"Pen","Name2":"White"}]
JSON
,true);
$result=array();
while($row=array_shift($ori))//Pretend that we're fetching record from DB
{
$result[$row["category"]][$row["orderID"]][]=array("Name"=>$row["Name"],"Name2"=>$row["Name2"]);
}
print_r($result);//This should be better
//But if you insist, this can help:
array_walk($result,function(&$v,$k){
$x=array("category"=>$k,"children"=>array());
array_walk($v,function($arr,$oid)use(&$x){
$x["children"][]=array("orderID"=>$oid,"children"=>$arr);
});
$v=$x;
});
print_r(array_values($result));