Tree's crevices suited plants and moles? (6,7)

I believe the answer is:

secret service

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'suited plants and moles?' is the definition.
I can't judge whether this definition defines the answer.

'tree's crevices' is the wordplay.
'tree's crevices' can be anagrammed to 'SECRET SERVICE'.
However, I'm unsure how this is indicated.

Can you help me to learn more?

(Other definitions for secret service that I've seen before include "Spies' department" , "Hush-hush organisation" , "MI5 or MI6 (informal)" , "Spying agency" , "Government agency" .)

I've seen this clue in the Sydney Morning Herald.

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