仅当其中一个字段是特定值时，LINQ才会对多个字段进行分组

I am trying to group a list by 2 fields (Category, then Vendor), but at different values. If the category is "01", sum all the cost. If the category is not "01", group by the category, and then by the vendor.I am trying to group a list by 2 fields (Catego