Selec List to Sub-Select List?

Use Case:  Adding new content, the User will be presented with a Category select list. Certain items on the select list will cause a secondary select list to invoke where the User can select a sub-Category.


Using Taxonomy I'm starting with a simple Category vocabulary and using relations to tuck in the child category. (attached)

When I develop the content type, how do I configure it to get the two select list per the use case?
category.PNG