Banana Trees start to appear from Woodcutting Level 50 and may chopped using the Woodcutting skill awarding the player Woodcutting XP or be grown via Farming from Banana Tree Seeds 
awarding the player Farming XP. After both harvesting options player also receives Tree Logs 
as well as Bananas 
, which give 50 Energy when consumed.
Tree Logs are especially useful for Crafting as well as Cooking, which give +1 heat when burned. This may be increased to +2 with the easy Woodcutting achievement perk.