Learner discovered in a tree (7)

I believe the answer is:

trainee

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

'learner' is the definition.
(I've seen this before)

'in a tree' is the wordplay.
'in a tree' anagrams to 'TRAINEE'.
But, I'm not clear how the anagram is indicated.

'discovered' acts as a link.

Can you help me to learn more?

(Other definitions for trainee that I've seen before include "One undergoing instruction" , "Person being instructed in work" , "novice" , "Aintree (anag.)" , "One taking instruction" .)

I've seen this clue in the Sydney Morning Herald.

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