Highest tree by the way (5)

I believe the answer is:

first

'highest' is the definition.
(thesaurus)

'tree by the way' is the wordplay.
'tree' becomes 'fir' (fir is a kind of tree).
'by the way' becomes 'st' (I've seen this in other clues).
'fir'+'st'='FIRST'

(Other definitions for first that I've seen before include "in dominant position" , "Top degree class" , "Position for gold" , "See 1" , "to begin with" .)

I've seen this clue in The Globe and Mail.

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