The best tree in the orchard (4)
I believe the answer is:
plum
This clue might be a double definition.
'the best' is the first definition.
(informal term for best or top-class)
'tree in the orchard' is the second definition.
'plum' can be an answer for 'tree' (plum tree is a kind of tree). I am unsure of the 'in the orchard' bit.
Can you help me to learn more?
(Other definitions for plum that I've seen before include "Pudding fruit" , "Fruit; something choice" , "Fruit < that's highly desirable" , "Fruit tree - of especial value?" , "Prize" .)