A Tree Tile is a map tile used to indicate a where a tree is growing. It has the same visual appearance as a Tree Seed Hole, but also has a tree of some type growing on that tile as an object -- because of this, you never actually see the hole in the tile.
As a tile type, a tree tile containing trees is a source of logs along with either tree seeds or apples, depending on the type of tree that was planted. In order to collect a log, you must use an axe to harvest the trees.
Apple trees can be harvested for apples by using a mallet on them if logs aren't explicitly needed. This is especially useful if apples are needed for apple pies but logs aren't needed.