Some possum active in tree (5)
I believe the answer is:
sumac
'tree' is the definition.
(I've seen this before)
'some possum active in' is the wordplay.
'some' says the answer is hidden in the clue (some parts of the word are used).
'SUMAC' can be found hidden inside 'possum active in'.
(Other definitions for sumac that I've seen before include "Spice" , "plant" , "Rhus tree" , "Shrub bright in autumn" , "Novelist" .)