Bean tree (5)
I believe the answer is:
carob
'bean tree' is the definition.
(carob is a kind of bean tree)
This is all the clue.
(Other definitions for carob that I've seen before include "(Seeds yielding) powder used as a chocolate substitute" , "Evergreen tree with edible pods" , "Chocolate substitute pod" , "St John's bread" , "Saint John's bread" .)