It has to be a small tree, like a miniature. Big ones eventually outgrow the containers. I have been starting small trees in pots for a while. These are nursery pots that are 3 ft across and 2 1/2 foot deep. By the third year if the tree has taken off, you have to transplant it. If you do severe pruning, you still have to root prune every few years. The pot, if a permanent item, has to be raised off the ground or have something under it so the roots do not go thru the pot into the ground.