How do you finish America land in the Simpsons DS Game?

In the America land level of The Simpsons DS game, you need to get 5 pieces of the Declaration of Independence. The map is in the shape of the United States and you need to go to all 4 corners of the map to get the pieces. Go to all the corners and you'll eventually find a tree with the last piece of the declaration of independence. Once you have all 5 pieces, return to the middle of the map and interact with the flag to finish the level.