Trees can be pruned into any shape or size.
The most common shape of a tree is a that of a standard: ie., a ball shaped structure (the head) on top of the stem (as opposed to a bush). For a garden tree you may want the head to be at least 1,5 to 2 meters above the ground to allow you to walk under the tree without bumping your own head.
Staking a tree while it is growing ensur es that the stem remains straight and creat es usable shade under the tree. While the tree is young it is possible to force it to grow straight by tying it firmly to a stake. At this stage all side branch es (below the head) should be removed leaving a bushy head at the top of the tree.
Maintain the bushy head in the shape of a circle. Cut off all branches that are growing too big for the circle. This allows the branches to grow from within the circle and to become denser. Too big a circle means less growth within the head or the ball.
As the tree grows taller the head should rise higher and higher above the ground. Branches below the head should continue to be removed. The head can be allowed to grow larger from its base point (at the bottom of the head) rather than growing down towards the ground. Allow branches on the side and above the ball to grow slowly enlarging the size of the head.
Once you have reached an acceptable height for the head of the tree, you can begin to remove all branch es which are growing downwards. Allow branch es to grow horizontally as this will expand the size of the head. You can also cut off all branch es that are shooting beyond the r es t of the head and ruining the general shape of the tree. Following this approach will transform the ball shaped head into a semi-circle with a flat base. As the tree grows larger it will loose the circular shape but maintain the flat base which provid es shade to sit under.