What is trevisano?

Nothing wrong at all with a bitter flavor in my book! Gives a great excuse for pairing with bacon or other smoked pork, as if I would need an excuse for that! But if a recipe calls for a bitter green and the cook doesn't know and subs a bland green, the end result would lack something.

Of course in Italy a bitter flavor is appreciated greatly. Not so much in N. America.

Trevisano raddicchio has a bitter flavor, so if you are trying to substitute it with another variety, perhaps an endive would work.

Trevisano literally refers to Treviso in the Veneto region of Italy. Both the round radicchio shape (Chiogia) and the oblong Treviso are now being grown successfully in California's Salinas Valley. The Chiogia shape is now more expensive than the Treviso. It used to be the other way round. Treviso resembles red endive so don't mix them up.

It's a kind of radicchio - a red lettuce, Radicchio comes in a "head" form like iceberg lettuce. Trevisano is an oblong radicchio