Strive to give height to a tree! (5)
I believe the answer is:
fight
'strive' is the definition.
(thesaurus)
'height to a tree' is the wordplay.
'height' becomes 'ht' (abbreviation).
'to a' is a charade indicator (letters next to each other) (I've seen this in other clues).
'tree' becomes 'fig' (fig tree is a kind of tree).
'ht' put after 'fig' is 'FIGHT'.
'to give' acts as a link.
(Other definitions for fight that I've seen before include "(Take part in) battle" , "Attack or engage in combat" , "Scrap" , "Conflict" , "Contend" .)