LINQ using NOT IN

How to create LINQ query fro the following SQL

Select * 
  FROM [DEV].[tss].[MERCHANT]
  Where 
  ParentID IS NULL
  OR
  ParentID NOT IN (Select distinct MerchantID FROM [DEV].[tss].[MERCHANT])

   var mm = context.MERCHANTs.OrderBy(e => e.MerchantID).Select(p => new Models.ViewModel.NEWVIEWMODEL.MerchantViewModel
            {
                MerchantID = p.MerchantID,
                MerchantName = p.MerchantName,
                ParentID = p.ParentID,
                CreatedBy = p.CreatedBy,
                CreatedDate = p.CreatedDate,
                ModifiedDate = p.ModifiedDate,
                ModifiedBy = p.ModifiedBy
            });

Any help using not in to the above query... appreciated.

Thank you