Providing assurance on the way to protect northern tree (10)

I believe the answer is:

confirming

'providing assurance' is the definition.
(confirm can mean to provide assurances)

'on the way to protect northern tree' is the wordplay.
'on the way' becomes 'coming' (synonyms).
'to protect' indicates putting letters inside.
'northern' becomes 'n' (abbreviation e.g. N. Ireland).
'tree' becomes 'fir' (fir is a kind of tree).
'n'+'fir'='nfir'
'coming' enclosing 'nfir' is 'CONFIRMING'.

(Another definition for confirming that I've seen is " Establishing truth".)

I've seen this clue in The Guardian.

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