I have model list and want to add list inside list without loop

var ItemModel = new ItemModels();
var modelItemList = new List<ItemModels>();
modelItemList = retitem.Select(x =>
{
return new ItemModels()
     {
SKU = x.SKU != null ? x.SKU : "",
SKU2 = x.SKU2 != null ? x.SKU2 : "",
Source = x.Source != null ? x.Source : "",                        
UPC = x.UPC != null ? x.UPC : ""   
      };
}).OrderByDescending(y => y.Barcode).ToList();

ItemModel.ItemList.Add(modelItemList);//it's not right way to add list inside list but i need that without loop.Is it possible?

//Inside Model
public class ItemModels
{
    public ItemModels()
    {
         ItemList = new List<ItemModels>();
    }
    public List<ItemModels> ItemList { get; set; }
}