How can I bind both selectlistitem and model objects to view?

See more:

MVC5

I want to update GroupTest table passing by idGroupTest.

What I have tried:

public ActionResult GroupTestUpdateById(int idGroupTest)
     {
         GroupTestUIModel groupTestUIModel = new GroupTestUIModel();

         MedicalTestBL medicalTestBL = new MedicalTestBL();

         var config = new MapperConfiguration(cfg =>
         {
             cfg.CreateMap<GroupTestModelBL, GroupTestUIModel>();
         });
         IMapper iMapper = config.CreateMapper();
         groupTestUIModel = iMapper.Map<GroupTestModelBL, GroupTestUIModel>(medicalTestBL.GroupTestUpdateById(idGroupTest));

         List<SelectListItem> selectTestListDDL = medicalTestBL.TestCategoryFormList().Select(x => new SelectListItem
         {
             Value = x.idTestCategory.ToString(),
             Text = x.TestCategoryName
         }).ToList();
         selectTestListDDL.Insert(0, new SelectListItem { Text = "Select", Value = "" });

         groupTestUIModel = new GroupTestUIModel()
         {
             selectTestCategoryType = selectTestListDDL
         };

         return View("GroupTestForm", groupTestUIModel);

     }

But I can't append both the dropdownlist items and GroupTest model object to `groupTestUIModel`. How can I do that?