Redirecting using regex wildcards – just middle part of URL

I am trying to work out how to redirect our old url structure to the new structure but am very confused. I did try to follow the documenation but it doesnt work.

Example of old URL structure:

wills-estates/writing-a-will/

New structure:

estate-planning/writing-a-will/

I have tried the following:

wills-estates/(.*)

to

estate-planning/$1 – ends up redirecting everything to estate-planning/)

and

estate-planning/* – ends up redirecting everything to estate-planning/)

and

estate-planning/(.*) – ends up redirecting everything to estate-planning/(.*

I cannot get it to work – what is the correct structure?