open this link
and go to about the 24 minute mark where explains bunchy top is a virus which means you need to remove the plant, no treatment is effective for plant viruses at this time. it shows the pest which spreads the virus but double you have that critter where you are, unless you live in Hawaii. That said any sucking insect that moves from plant to plant could spread the disease. If this is a new plant it may have been shipped to you diseased, if it is an old existing plant I would watch it to see if it doesn't recover, could just be a fluke of nature and not the virus, so it may resolve itself. inspect under the leaves for small insects and consider spraying with an insecticide for that pest and has been approved for use on bananas.
if it is a virus then you need to dig it up and burn it on site if you are allowed to burn where you are. If not double bag it in plastic garbage bag and send to land fill, don't compost it you can't get the pile hot enough to reliably kill viruses. Don't replant there any time soon.