Senior citizen plants tree on isle (8)

I believe the answer is:

alderman

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'senior citizen plants tree on isle' is the definition.
I can't judge whether this defines the answer.

'tree on isle' is the wordplay.
'tree' becomes 'alder' (alder is a kind of tree).
'on' is a charade indicator (letters next to each other).
'isle' becomes 'man' (the Isle of Man is an example).
'alder'+'man'='ALDERMAN'

Can you help me to learn more?

(Other definitions for alderman that I've seen before include "Civic officer" , "Former civic dignitary" , "In England and Wales, a former senior local councillor" , "Member of an English city council" , "Bigwig" .)

I've seen this clue in The Sun.

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