Função recursiva

NetWorkService.php

<?php namespace App\Services;

use App\User;

class NetWorkService {
  public function getUsers( $sponsor )
  {
      $users = User::where('sponsor', 'LIKE', '%' . $sponsor . '%')->get();

      foreach($users->toArray() as $user) {

          $network = (array) json_decode($user['sponsor']);

          $list[] = [
              'id'        => $user['id'],
              'login'     => $user['name'],
              'email'     => $user['email'],
              'name'      => $user['nome'],
              'network'   => [
                  'nivel' => $network['nivel'],
                  'pos'   => $network['pos']
              ],
              'users' => $this->getUsers($user['name'])
          ];
      }

      return ($users ? $list : null);
  }
}