You’re looking for a double return tread. Double returns are sold by the throat length, which is the length between the two returns on the back of the tread.
These are the standard 1” double return oak treads:
https://www.stair-treads.com/double-return-traditional-1-red-oak-stair-tread-prefinished-natural-or-stained.html
And these are the retro-fit double return treads:
https://www.stair-treads.com/double-return-retro-fit-red-oak-stair-tread-prefinished-natural-or-stained.html
This link better exmplains “throat length”:
https://www.stair-treads.com/faq/standard-stair-tread-dimensions.html
And more information on types of staircases is available here:
https://www.stair-treads.com/types-of-staircases
If you don’t see the throat length you need, give us a call at (866) 429-0979 and we can configure it for you