Binding Nested List to DropdownListFor with List

Question

I want to pass a nested list (List<OptionValueList>) to a View; then render each corresponding List<OptionValue> inside @Html.DropdownListFor.

Class:

public class OptionValue
{
   public int OptionID { get; set; }
   public int ValueID { get; set; }
   public string ValueName { get; set; }      
}
public class OptionValueListList : List<OptionValueList> { }
public class OptionValueList : List<OptionValue> { }   

I fill the class OptionValueListList from db, but I couldn't adapt it in SelectListItem in order to bind data to @HtmlDropdownListFor.

Below is my View:

    @model Program.Models.OptionValueListList

    @foreach (var item in Model) /*List<OptionValueList>*/
    {
         foreach (var y in item) /*List<OptionValue>*/
         {        
  @Html.DropDownListFor(m=>y.ValueID, new SelectList(@ViewBag.x, "Value", "Text"), "Option Values")
       }
     }

And below is where I try to pass data and could not bind properly as it renders same dropdownlistfor for 18 times:

   OptionValueListList o = new OptionValueListList();
   o = pr.GetOptionsForProduct(id);
   foreach (var item in o)
   {
        foreach (var i in item)
        {
             List<SelectListItem> li = new List<SelectListItem>();
             li = (from c in item
                  select new SelectListItem
                  {
                        Text = c.ValueName,
                        Value = c.ValueID.ToString()
                  }).ToList();
              ViewBag.x = li;
         }  
    }

The problem in ViewBag.x = li; Where should I put this Viewbag? Thanks.