@Html.DropDownList("gid", (SelectList)Model.Groups, new { style = "width:90%; border:1px solid", id = "ddlGroup", data_bind = "options: Groups, optionsText: 'Text', optionsValue: 'Value'" })

function CascadingDDLViewModel() {
        this.Groups = ko.observableArray([]);
        this.Stores = ko.observableArray([]);
    }

        this.Groups = ko.observableArray(objVM.Groups);
        this.Stores = ko.observableArray(objVM.Stores);

 public class StoreData
    {
        public SelectList Regions { get; set; }
        public SelectList Groups { get; set; }
        public SelectList Stores { get; set; }
}