Can we put sub category?

There is option to put a category under a parent category. would that be possible to select the subcategory after selecting category? It help reduce the number of drop down items.

Like if we keep, category and sub-getegory (in parent) in one drop down list it will be difficult to choose and find the right category. But when we keep different drop down for sub-category it would be easy to find and select the righ category.

Single Drop down                                                  with Sub-Category

He, She, Ram, Sonu, Geeta                                    He->Ram,Sonu.  She->Geeta