When the pseudostem of a banana is regularly damaged, pups are often produced. Year after year, they'll continue to multiply, particularly with the underground corm maturing and growing further in size.
Cincinnana has a Flickr photostream which provides a pretty awesome example of the basjoos being cut back every winter and what happens in the spring. Check out the final 3 albums:
https://www.flickr.com/photos/110357684@N02/sets/