groupbydisplaying listview get data from api

i want get data from api ....and have dynamic data.means i have many Title that each title have different subtitle.for exmaple one title had two subtitle and another had 7 subtitle. how can i change it... i just got it for one title and one subtitle.

     List<OrderAppViewModel> Items = new List<OrderAppViewModel>{
                new OrderAppViewModel(_order.Find(a => a.CodeTitle == i).TitleName, CodeSubject, _order.Find(a => a.CodeTitle == i).BackgoroundColor){

            new OrderTarrif { DisplayName = _ordert.Find(a => a.Name == "insert").DisplayName,
                Price = _ordert.Find(b => b.Name == "insert").Price }

                , }
             };
            Contents = Items;