Tree when developed bears a type of apple (5)
I believe the answer is:
eater
'type of apple' is the definition.
(I've seen this before)
'tree when developed bears a' is the wordplay.
'when developed' indicates anagramming the letters.
'bears' is an insertion indicator (some letters carry or bear others).
'tree' anagrammed gives 'eter'.
'eter' enclosing 'a' is 'EATER'.
(Other definitions for eater that I've seen before include "Taker of food" , "Fruit (but not a cooker)" , "Apple, perhaps" , "Consumer at table" , "Type of apple" .)