European trees are rubbish (7)
I believe the answer is:
eyewash
'rubbish' is the definition.
(both can mean nonsense)
'european trees are' is the wordplay.
I cannot really understand how this works, but
'european' could be 'e' (abbreviation e.g. EU) and 'e' is present in the answer.
'are' could be 'was' (being is a kind of being) and 'was' is found in 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 "Nonsense (colloq.)" , "Rhubarb" , "Balderdash" , "Fiddlesticks" , "Optic lotion - nonsense!" .)