<label for="entity_id">Asignar Entes</label>
  <select id="ms" name="entity_id[]" multiple="multiple">
     @foreach($entities as $e)
       <option value="{{$e->id}}">{{$e->name}}</option>
     @endforeach
  </select>

public function store(Request $request)
{
    $user= new AppUser();
    $user->name=$request->name;
    $user->email=$request->email;
    $user->entity_id=$request->entity_id;
    $user->role_id=$request->role_id;
    $user->password=bcrypt($request->password);

    if($user->save()){

     return redirect()->route('users.index', $user->id)
         ->with('info', 'Usuario guardado con éxito');
    }
    else{
        return redirect()->route('users.index')
         ->with('info', 'No se guardó el usuario');
    }
}