Cannon part put right inside tree (6)
I believe the answer is:
breech
'cannon part' is the definition.
(I've seen this in another clue)
'right inside tree' is the wordplay.
'right' becomes 'r' (abbreviation).
'inside' is an insertion indicator.
'tree' becomes 'beech' (beech is a kind of tree).
'r' inserted inside 'beech' is 'BREECH'.
'put' acts as a link.
(Other definitions for breech that I've seen before include "One's behind" , "Back part of a gun barrel" , "Opening for loading a gun" , "Back part of rifle" , "Describing a delivery in which the baby is inverted" .)