Now when users go to "Mens Clothing" they see all the items, then they select one "Jeans" they want to buy and they are redirected to "Jeans" Page. Now they add items to their basket and they are redirected to "Basket" Page.
Now I have a button on "Basket" page called "Keep Shopping". When they click I need to redirect them to Mens Clothing Product List instead of Home Page.
Now you say you want to redirect to the "Mens Clothing" page, but you have to determine why you want to redirect to that page. If it always is that page, then hardcode that:
Response.Redirect("Shop/Categories/Mens-Clothing");
Though when the page you want to return to depends on what item was added to the basket, you need to realize what page you want to redirect to and how the relation of that page is with regard to the item.
The Basket page knows what item is being added to the basket. If you for example want to redirect to the category page for that item, look up the category this item is in, and redirect to that page:
Response.Redirect("Shop/Categories/" + item.Category.Name);
Although this will redirect you to the "Jeans" page, because that is the choosen item's category.
Now it looks like you want to redirect to the parent category of the category the item is in. Then you user that:
Response.Redirect("Shop/Categories/" + item.Category.ParentCategory.Name);
Or whatever your data model looks like.