From the Super Mario Wiki
The Beanstalk is an enormous plant located in Fungi Forest in Donkey Kong 64 that grew from a small, pink seed found by Tiny Kong. Tiny finds the seed inside a tree stump, after she defeats a large group of Purple Klaptraps. After that, she must plant it in some fertile soil, where it grows almost instantly. At the top of the Beanstalk is a Golden Banana, which Tiny must acquire by getting a ride from Squawks the Parrot after shrinking.