Emergency treatment to make tree steady (5,3)
I believe the answer is:
first aid
'emergency treatment' is the definition.
(I've seen this in another clue)
'tree steady' is the wordplay.
'tree' becomes 'fir' (fir tree is a kind of tree).
'steady' becomes 'staid' (I am not sure about this - if you are sure you should believe this answer much more).
'fir'+'staid'='FIRST-AID'
'to make' acts as a link.
Can you help me to learn more?
(Other definitions for first aid that I've seen before include "Immediate help for the sick or injured" , "Basic medical help" , "Immediate treatment for the wounded" , "dressing" , "Emergency procedure" .)