Grouping of list values

Question

Hi,

I have a list with users and orders in one list like below    

user 1	order1
user 1	order2
user 1	order3
user2	order2
user2	order3

From here I have form as user1 with his orders list (1,2,3) as one group and user2 as (2,3) with another in C# 

Thanks