Adding New items to subcategory

Ladies/Gents,

Is there a way to add a new item and specify which subcategory that it can be attached to? I've notice that the categories, subcategories are not sorted and organized to its parent field.

Example:
I have already

category x
Sub-category: login issue

and

category y
subcategory: login issue

Now I create an item that shows "need username/password" .. but I just want to attach this item to category Y under the subcategory login issue..

This is still possible but its a trial and error process as both subcategory are shown on the list as "login issue" but neither shows which "login issue" does that main category belongs to..

Can anyone help me check, what is the best way of organizing an item under the right category, subcategory, etc.

Thanks,
htran