Tree subdued for medical treatment (5,3)
I believe the answer is:
first aid
'medical treatment' is the definition.
(I've seen this before)
'tree subdued' is the wordplay.
'tree' becomes 'fir' (fir is a kind of tree).
'subdued' becomes 'staid' (I've seen this in another clue).
'fir'+'staid'='FIRST-AID'
'for' acts as a link.
(Other definitions for first aid that I've seen before include "Emergency procedure" , "dressing" , "Initial treatment given to injured person before arrival of doctor" , "Preliminary medical help pending arrival of doctor" , "Immediate medical help pending full treatment" .)