If the tree is barren, it’s no good (9)
I believe the answer is:
fruitless
'no good' is the definition.
Both the answer and definition are adjectives. Perhaps you can see an association between them that I don't see?
'if the tree is barren it's' is the wordplay.
I cannot really understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
'it's' could be 'es' ('e' can mean 'electronic' which is similar to 'IT') and 'es' 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 fruitless that I've seen before include "Unprofitable" , "Such an unhealthy diet" , "Futile; barren" , "Vain" , "Ineffectual" .)