Close, but no cigar.
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The cherry on the top is an allusion to icecream sundays and similar deserts, sweets, where the cherry there was one cherry on top, the best, the sweetest part.
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So the cherry on the top is just the best part. Expected, but best.
You win, yes, that is great, but the cherry on the top is that you get .... as well.
For me the new house was wonderful, but the cherry on the top was that it was a ten-minute commute to work.