Category Vs Sub Category Vs Product Group

Currently, we have a task where we can create Category and Child Category (ideally subcategory). With this setup, upon creation of service request in HR Help Desk, we could see all the category and sub category displayed in alphabetical order.

Is there a way to display the list with Category and respective sub category in order.

If that's not the case, can we use Category and Product Fields to make use of this functionality.

Eg, If we select Benefit in category, corresponding Sub Category should be listed in Product Field eg, Disability etc.

Are any alternate solution to handle this request will be really helpful.