Left English tree, showing restraint (5)
I believe the answer is:
leash
'restraint' is the definition.
(I know that leash is a type of restraint)
'left english tree' is the wordplay.
'left' becomes 'l' (common abbreviation).
'english' becomes 'E' (abbreviation).
'tree' becomes 'ash' (ash is a kind of tree).
'l'+'e'+'ash'='LEASH'
'showing' acts as a link.
(Other definitions for leash that I've seen before include "Bind" , "Spanish city famous for swordmaking" , "Restraint for a dog" , "Rope to control dog" , "Dog lead" .)