When I tried to create a new world, I wanted it to be all jungle. I chose "Jungle" as the option. Then I created the world, and there were no big jungle trees. I checked the F3 screen, and it said I was in a JungleEdge biome. I then deleted that world, made a new one with the same name, I double checked to make sure it was Jungle, and I got another JungleEdge.