include category dropdown in search bar

I have made a category of “professionals” (e.g.: lawyers, therapists, accountants, etc.) and want to have it as a dropdown in the main search bar. I see you can do it for “places”, e.g.: hotels, people, events and want to be able to have my professionals in the dropdown list.

I have added 2 screenshots, 1 is the standard demo showing the dropdown for places on the left, and the other image is what I’m working on, I currently have a categories list, but would love it to be a dropdown coming from the same place as the 1st screenshot (demo image).

I am trying to keep all listing content and pricing the same, so if 1 changes, they all change at once, without having to manually go into each category. What is the best way to implement this?