.OrderBy(y => y.Year).ThenBy(m => m.Month);

How to set descending order?

EDIT:

I tried this:

var result = (from dn in db.DealNotes
                         where dn.DealID == dealID                         
                         group dn by new { month = dn.Date.Month, year = dn.Date.Year } into date
                         orderby date.Key.year descending
                         orderby date.Key.month descending
                         select new DealNoteDateListView { 
                             DisplayDate = date.Key.month + "-" + date.Key.year,
                             Month = date.Key.month,
                             Year = date.Key.year,
                             Count = date.Count()
                         })
                         //.OrderBy(y => y.Year).ThenBy(m => m.Month)
                         ;

And it seems working. Is it wrong to use orderby twice like I used it here?