Use the following steps to get to level 50. Build a machine gun at the exit nothing else. Build a second machine gun when you have the money. Also, build a healing weapon. Turn both machine guns to Gatling guns and start building a third Gatling gun. Make sure they are blocking the exit. After building at least thirteen of these, start building chain lightnings, more apple trees, and healing weapons built near or as close as possible to the exit. Save some money to build lots of nuclear barrels.
Play at score screen
Start a game and let the worms get the apple. When they reach the exit press [Esc] just when you lose. Put the pointer off screen, then type at least ten letters. You will hear a sound. Move the pointer back to the screen and you will have a tower.