You would say 5 pieces of fruit. 'I have 5 pieces of fruit. I have 2 bananas and 3 oranges.' 'How many apples do you have?' 'I have none. I have 5 pieces of fruit, none of which are apples'

You say "five pieces of fruit". Fruit is a collective uncountable noun here. If you say "fruits" (which is uncommon), then you mean "different types of fruit". In your example, you have two fruits: banana, and orange.