Passion Tree, associated with ecstasy (4)
I believe the answer is:
fire
'passion' is the definition.
(fire is a kind of passion)
'tree associated with ecstasy' is the wordplay.
'tree' becomes 'fir' (fir is a kind of tree).
'associated with' says to put letters next to each other.
'ecstasy' becomes 'E' (informal term for the drug).
'fir'+'e'='FIRE'
(Other definitions for fire that I've seen before include "Sack; conflagration" , "Inspire" , "Sack; discharge (a gun)" , "Dismiss; bake in a kiln" , "... or combustion" .)