Set CUSTOM_RELATIONSHIP_1 for products

[HappyHippo]

Hi!,
Currently a bundle product can not be inside another bundle product...it gives  me error "Recursion was detected. Ensure that a bundle product does not include itself as one of the bundled products ".

Can this problem be solved by giving CUSTOM_RELATIONSHIP_1 to the products.
In admin panel; how do we set custom relationships(CUSTOM_RELATIONSHIP_1,CUSTOM_RELATIONSHIP_2 etc.) to products?
In admin panel; how to add our own products_type? Where does it store in database?
In which table do you store relation_type that is in products_to_products table?

Thank you very much!