And now... Number 2: the log
The lack of roots and sometimes branches is a sure sign of a log. There is some philisophical debate on this subject, though. If a lumberjack drops a log in the forest and no one's around to see it, when does it stop being a tree? This has been deemed a "silly argument" and dismissed by the national tree recognizer's commitee, but you may want to take into account
Some logs are dropped in the forest, some are dropped into rivers and carried downstream. But wherever they are, you should now be able to see them from quite a long way away and recognize "That's #2, the Log!".