Being unrealistic about one bit of business, I celebrate (10)

I believe the answer is:

idealising

'being unrealistic' is the definition.
(being idealistic)

'one bit of business i celebrate' is the wordplay.
'one' becomes 'i' (Roman numeral).
'bit of business' becomes 'deal' (I've seen this in another clue).
'celebrate' becomes 'sing' (I've seen this before).
'i'+'deal'+'i'+'sing'='IDEALISING'

'about' is the link.

(Another definition for idealising that I've seen is " wearing rose-tinted spectacles?".)

I've seen this clue in The Times.

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