Embitters wild beast behind tree (9)

I believe the answer is:

acerbates

'embitters' is the definition.
('acerbate' can be a synonym of 'embitter')

'wild beast behind tree' is the wordplay.
'wild' indicates anagramming the letters.
'behind' means one lot of letters go next to another.
'tree' becomes 'acer' (I've seen this in other clues).
'beast' is an anagram of 'bates'.
'bates' after 'acer' is 'ACERBATES'.

(Another definition for acerbates that I've seen is " Makes sour".)

I've seen this clue in The Mirror.

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