Clear above top of trees (5)
I believe the answer is:
overt
'clear' is the definition.
(thesaurus)
'above top of trees' is the wordplay.
'above' becomes 'over' (I've seen this before).
'top of' indicates taking the first letters.
The first letter of 'trees' is 't'.
'over'+'t'='OVERT'
(Other definitions for overt that I've seen before include "Open,up front" , "This is not hard to see" , "Plain and obvious" , "Not concealed - public" , "Voter (anag.)" .)