How to cache asp.net mvc data using Cache obect

I am using data caching in my asp.net application. This is my frontend for ICacheProvider.cs

public interface ICacheProvider
{
    object Get(string key);
    void Set(string key, object data, int cacheTime);
    bool IsSet(string key);
    void Invalidate(string key);
}

      

        
        
        
      

    

This is how I use caching in services.

public List<EmployeeLookUp> GetEmployeeLookUp(RecordStatusEnum recordStatusEnum, int locatioId)
    {
        var status = (int)recordStatusEnum;

        var employeeData = Cache.Get("EmployeeLookUp") as IEnumerable;

        if (employeeData == null)
        {
            var result = MyDb.Employee.Where(w => w.Status == status && w.LocationId == locatioId).ToList().Select(s => new EmployeeLookUp()
            {
                EmployeeId = s.EmployeeId,
                DepartmentId = s.DepartmentId,
                EmployeeValue = string.Format("{0}{1}{2} {3} {4}", "[", s.CustomEmployeeId, "]", s.FirstName, s.LastName)
            }).ToList();

            if (result.Any())
                Cache.Set("EmployeeLookUp", result, 30);

            return result;
        }

        return (List<EmployeeLookUp>) employeeData;
    }

      

        
        
        
      

    

In the controller, I am using the returned employees like this.

 public ActionResult Index()
    {
        var employees = _employeeServices.GetEmployeeLookUp(RecordStatusEnum.Active, User.GetCemexUser().LocationId);
        employees.Insert(0, new EmployeeLookUp() { EmployeeId = -1, EmployeeValue = "All" });

        var complexRosterViewModel = new ComplexRosterViewModel
        {
            EmployeeList = new SelectList(employees, "EmployeeId", "EmployeeValue"),
            ListEmployeeGroups = new SelectList(_employeeGroupServices.GetEmployeeGroup(RecordStatusEnum.Active, User.GetCemexUser().LocationId), "EmployeeGroupId", "Value"),
            ListDepartments = new SelectList(_departmentService.GetDepartments(RecordStatusEnum.Active,User.GetCemexUser().LocationId),"DepartmentId","Value")
        };

        return View(complexRosterViewModel);
    }

      

        
        
        
      

    

Now my problem is that when I reload the page multiple times, the extra "Everyone" option I added to the employee picklist was added to the cached object ("EmployeeLookUp") multiple times. How is this possible? I do not want the "All" option to be cached.