There's a tree in the middle of the road! (6)
I believe the answer is:
street
'road' is the definition.
(I know that road can be written as street)
'there's a tree in the middle of the' is the wordplay.
'there's' means one lot of letters goes inside another (I've seen this in other clues).
'in the middle of' becomes 's' (I can't justify this - if you can you should give a lot more credence to this answer).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
's'+'t'='st'
'tree' going within 'st' is 'STREET'.
Can you help me to learn more?
(Other definitions for street that I've seen before include "Acceptability amongst the 'with it' young" , "Thoroughfare lined with buildings" , "See 7" , "Road lined with buildings" , "See 14" .)