Laravel pluck nested collection to root collection

I have a data structure like you can see in the picture above.
I want some fields in the root collections, but I don't know how can I can get that.

public function index (Request $request) {
    $draw = $request->get('draw');
    $start = $request->get('start');
    $length = $request->get('length');

    $order = Order::with('user');
    $total_order = $order->count();
    $orders =  Order::with('user')->offset($start)->limit($length)->get();

    /*$draw = ceil($total_order/$length);*/
    return response()->json([
        'draw' => $draw,
        'recordsTotal' => $total_order,
        'recordsFiltered' => $total_order,
        'data' => $orders,
    ]);
}