Each record has to have it's won ID to uniquely identify it. You're treating your existing ID column as a primary key for the table when it is, in fact, a foreign key into another table.
The solution is pretty easy. Add a new identity column to the table.
ID Frequency_Set_Id Item_Name
1 1 Butter
2 1 Oil
3 1 Apple
4 2 Cookies
5 2 Orange