The joke of two stories

There is a mental hospital on Wutai Mountain. Because there are too many people inside, the dean is going to manage the building separately. So he called everyone to choose a director. There are three floors, so he took three kinds of fruits. He first took out a banana and asked, "What is this?" One person answered "banana", and the dean said, "OK, you are the director on the first floor!" The dean took out another watermelon and asked what it was. The director on the second floor was also born. Finally, the dean came to choose the director on the third floor, and he also took out the same ... the same thing ... red, round, autumn, sweet and hungry. What is this? I forgot ~ Please remind me ~ ~ ~