@using (Ajax.BeginForm("SaveProduct", "Home",
    new { id = idgr, mTab = mtab, IdTree = idTree, Parent_id = parentId, Typ = typ },
    new AjaxOptions
    {
        UpdateTargetId = "#event_result",
        HttpMethod = "POST",
        InsertionMode = InsertionMode.Replace,
    },
    new {enctype = "multipart/form-data"}))
{

  .........................................................
    <input type="file" value="Выбрать файл..." name="btnFile" id="btnFile" />
    <input type="submit" value="Сохранить" id="btnSubmit"/>
         
}

        public PartialViewResult SaveProduct(int? id, string mTab, int IdTree, int Parent_id, string Typ, FormCollection frm, HttpPostedFileBase btnFile)
        {

................................
            modelTA = GetDataForGrid(IdTree, Parent_id, Typ);
            return PartialView("Table", modelTA);
        }