how to display records from database by creating sublist within a list in asp.net using c#

Well, let's think of the problem in a different way, shall we?

You're displaying a list of watches with a category. So...group by category, and then sort by whatever is relevant.

I don't have an IDE with me...but something like this should work:

var watches = from w in datacontext.Watches
              group w by w.Category into g
              select new Watch { Category = g.Key, Watches = g };

Now, your watches variable contains x groups of watches (however many categories you have).

You can iterate over this list with a simple foreach as such:

foreach (watchGroup in watches)
{
   // print a header or something
   // Console.WriteLine(watchGroup.Key);
   foreach (watch in watchGroup.Watches)
   {
      // do something here
      // Console.WriteLine(watch.Name);
   }
}

Of course, you'll need to wrap the iteration part above in the appropriate <% %> tag syntax if you're using it on the page. In MVC, you can store the groups into your model on the page or even in the ViewBag.

EDIT: you can get more infos on LINQ here: MSDN[^]

Cheers.