From the Super Mario Wiki
Donkey Kong Banana Bunch is a minigame in Mario Tennis for the Game Boy Color. A variation of tennis, the premise is to hit Banana panels with a tennis ball as Donkey Kong. Points are scored for every Banana (or banana bunch) hit. One banana is equal to one point, while 3 bananas in a bunch is equal to 3 points. He can keep playing until he misses in the challenge mode. When the high score of 60 is beaten, the Jungle Court is unlocked. The music for this minigame is a remix of the original Donkey Kong Country theme. It's music is also shared with the Jungle Court.