Product categories in Wordpress

[sKunKbad]

I have made a custom post type for products, and am using a custom taxonomy for the product categories. The thing that I am wondering about is that sometimes a product category is a parent, and sometimes a child, but sometimes both. For instance, if you have a top level category named shoes, then you might have a sub category named Nike. However, Nike also has shirts, so you could say that shoes and shirts were both subcategories of Nike. Do you know what I'm saying? It's like there is no real parent to child relationship, but they are both parents and both children of each other. How do you handle this type of situation?