Category repetition Issue

Question

I'm working on list box "<SELECT>" using .net MVC but I faced problem from many days 

Subcategory successfully fetch but Main category Repeat with every subcategory 

in <optgroup>

 

 

"Query perform by ADO.Net Entity Framework"

 

List<tblSubcategory> list = (from x in context.tblSubcategories where (x.Isactive == true) orderby x.CategoryId descending select x).ToList();

return list;