asp.net mvc - Using C# Entity Framework how I can display "Select ALL" option in my combobox -

i working on mvc 4.0 entity framework. please consider following action method , me how can display "select all" text in combobox.

    [httppost]     public actionresult loadcustomer()     {         userpersistence user = ((userpersistence)session["ultuser"]);         ilist customer = dbcontext.customergroups.select             (                 e => new                 {                                             id = e.customergroupcode,                     name = e.customergroupcode + "-" + e.name,                     cty_iso = e.cty_iso                 }                 ).where(e => e.cty_iso == user.cty_iso).tolist();         return new jsonresult { data = new selectlist(customer,"id", "name") };     } 

i attached jsonresult combobox working fine problem how can display "select all" text in combobox.

in view i'm using telerik mvc combobox show list:

@(html.telerik().combobox()  .name("customercode")  .htmlattributes(new { @class = "dropdown", style = "width:90%;" })  .autofill(false)  .databinding(binding => binding.ajax()  .select("loadcustomer", "ccstypes").cache(true))  .filterable(filtering =>  {       filtering.filtermode(autocompletefiltermode.contains);  })  .highlightfirstmatch(true)                                          )     

thank you.