In English, "fruit" is an uncountable noun and can technically be singular or plural like the word "fish". Usually to make it clear something in the context will indicate "a" fruit versus "some" fruit. You can also make it plural and use "fruits" like "fruits and vegetables" but even though a "fruit basket" may contain several types of fruit, we wouldn't call it a "fruits basket." To further complicate things, some types of fruit, like grapes, have many pieces or, like an apple, can be cut into pieces so, although a whole apple is a piece of fruit (from a selection of fruit(s) in a basket), a singular grape or slice of apple is too. Not sure if that's helpful.