Rather than removing duplicates you should just not add them in the first place. As OriginalGriff has said, we don't know how you define "duplicate"
In this code I am assuming you don't want items with the same prodID
foreach (var data in product)
{
if (!cart_list.Any(p => p.prodID == data.prodID))
{
cart_list.Add(data);
}
}
Unrelated but don't use static for your cart. I know it looks like it is working but that 's because you only have one user....you. Browse your site from two different browsers and you'll see that all your users share a single cart. Use the Session to store the cart instead.