This is an identification program for trees of Northeastern and Central North America. Fill out the form as best as you can and you'll find which trees match. It's better to start with a few characteristics you are sure about, then add more as needed. Use the "Back" button to go back and add (or subtract) characteristics. If you want to see all the trees in the database, simply hit "Identify" without checking any boxes. Fully identifying the tree is up to you.
Some books that can help include:
Tree Leaf Characteristics: see this image (from Wikipedia) for a useful description of the leaf terminology used below.