Bird a long time in top half of tree (7)
I believe the answer is:
tanager
'bird' is the definition.
(tanager is a kind of bird)
'a long time in top half of tree' is the wordplay.
'a' becomes 'an'.
'long time' becomes 'age' (an age is a period of time).
'in' is an insertion indicator.
'top half of tree' becomes 'tr' (I can't explain this - if you can you should give a lot more credence to this answer).
'an'+'age'='anage'
'anage' placed within 'tr' is 'TANAGER'.
Can you help me to learn more?
(Other definitions for tanager that I've seen before include "Songbird of the bunting family" , "American songbird" , "A bird" , "South American singer" .)