Put forth effort and figure to get up in a tree (5)

I believe the answer is:

exert

I'm a little stuck... Click here to teach me more about this clue!

'put forth' is the definition.
(thesaurus)

I don't understand how the remainder of the clue works.

(Other definitions for exert that I've seen before include "Bring into operation" , "Work very hard" , "Cause (oneself) to make a strenuous effort" , "Make a great effort" , "Strain" .)

I've seen this clue in the Evening Standard.

Want a hint initially instead of a full solution? Install my app