Salt found in tree top (8)
I believe the answer is:
pinnacle
'top' is the definition.
(pinnacle is a kind of top)
'salt found in tree' is the wordplay.
'salt' becomes 'nacl' (NaCl is the chemical formula for sodium chloride).
'found in' is an insertion indicator.
'tree' becomes 'pine' (pine is a kind of tree).
'nacl' placed inside 'pine' is 'PINNACLE'.
(Other definitions for pinnacle that I've seen before include "The highest level" , "Topmost point" , "Highest point of success" , "Place inn on the very top" , "Apogee" .)