The French tree reveals restraint (5)
I believe the answer is:
leash
'restraint' is the definition.
(I know that leash is a type of restraint)
'the french tree' is the wordplay.
'the french' becomes 'le' ('the' in French).
'tree' becomes 'ash tree' (ash is a kind of tree).
'le'+'ash'='LEASH'
'reveals' acts as a link.
(Other definitions for leash that I've seen before include "Rope or chain restraint" , "Line for controlling a dog" , "Animal restraint" , "Rope to control dog" , "Rope used to restrain an animal" .)