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

I believe the answer is:

exert

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'put forth effort' is the definition.
(I've seen this in another clue)

I can't explain the remainder of the clue.

(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.

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