English trees are rubbish! (7)
I believe the answer is:
eyewash
'rubbish' is the definition.
(both can mean nonsense)
'english trees are' is the wordplay.
I cannot quite understand how this works, but
'english' could be 'e' (abbreviation) and 'e' is found within the answer.
'are' could be 'was' (being is a kind of being) and 'was' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for eyewash that I've seen before include "Balderdash" , "Slangy nonsense or optical cleanser" , "Pupils may benefit from this" , "Nonsense (informal)" , "Rhubarb" .)