According to Express, separating the bananas and wrapping each stem individually with plastic wrap will allow them to stay fresh for up to two weeks. This method traps the tops of the fruit, which is where ethylene gas is released. Because the spread of this ripening gas is controlled and not exposed to the other bananas, this slows down the ripening tremendously. Furthermore, you don’t need much plastic wrap at all.
You can use plastic wrap or cling wrap, and just need a small square for each banana to completely cover the tops. Business Insider states that while you definitely can try leaving the bananas in a bunch and wrapping the stems as a whole that way, this risks not working if there’s one banana riper than the others. Their higher levels of ethylene gas will emit into the other bananas, plastic wrap or not. The saying “one bad apple spoils the bunch” is correct in this sense.