you should define the ViewBag in your Post Action 

[HttpPost]
        [ValidateAntiForgeryToken]
        public ActionResult LeaveMapping(CompanyViweModel model)
        {

            try
            {

                ViewBag.company = HttpContext.Session.GetInt32("companyid");
                ViewBag.companyname = HttpContext.Session.GetString("companyname");
                ViewBag.leavetype = _listrepository.GetLeaveType();

                tb_company_leave_master compamnylv = new tb_company_leave_master();
                compamnylv.num_days = model.num_days;
                compamnylv.num_leave_type = model.num_leave_type;

my mean the highlighted line