The above answers are correct and I would like to add more information. The reason that the tree is dwarfed or minature is because of the conditions it has been grown in. They are grown in small pots so that the root system is confined and unable to sustain a normal sized tree or shrub thus dwarfing it's size. This is considered an art and takes skills and knowledge to obtain the natural look of a large tree in minature form.  For many this is a hobby and takes some time and experience to perfect. It is important to know which branches to keep and which to remove. One way of training the branches into the desired shape is by using wire to wrap around the branch and controlling the way or direction in which it grows. The idea of bonsai is to see it's shape and structure.