Outdo frantic bigwigs (3,7)

I believe the answer is:

top bananas

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'bigwigs' is the definition.
('top banana' can be a synonym of 'bigwig')

'outdo frantic' is the wordplay.
'outdo' becomes 'top' (I've seen this in another clue).
'frantic' becomes 'bananas' (I am not sure about this - if you are sure you should believe this answer much more).
'top'+'bananas'='TOP BANANAS'

Can you help me to learn more?

I've seen this clue in The Everyman puzzle in The Observer.

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