Some hilltop, in essence, for trees (5)
I believe the answer is:
pines
'trees' is the definition.
(pine is a kind of tree)
'some hilltop in essence' is the wordplay.
'some' indicates the answer is hidden within the clue (some parts of the word are used).
'PINES' is hidden within 'hilltop in essence'.
'for' acts as a link.
(Other definitions for pines that I've seen before include "Yearns for evergreen trees?" , "Yearns for the conifers" , "Longs for or languishes" , "Longs for evergreen trees" , "Coniferous trees" .)