Separating categories and sub-categories into separate drop-down menus

Hi,

I’ve created separate custom post types for each of my different place types (e.g., Accommodation, Entertainment, Travel, etc.) as it makes the searching process neat as I can have separate dropdown menus for the post type, and then the categories within that post.

For administrative purposes and so that I can easily show all place types on the same map, I’m considering migrating all of these custom post types into the single ‘Place’ post type, and then creating individual categories and sub-categories to categorise all places in the same manner.

One downfall I’m finding is that I can’t seem to create separate drop down menus for ‘Categories’ and ‘Sub-categories’ (see image attached). So instead of having a single drop-down as in the attached image, I’d like them in 2 separate drop-downs. Is this possible to do?

Thanks!
Andrew