Right, we need to read up on Newton's three Laws of Motion and his Law of Gravity before we go any further on this project.
50 cms is the diameter of the top of the pot. The base may be somewhat smaller, or it may not be. Given that the pot is cylindrical, the diameter will be only one twelfth the size of the total height of your tree. Your tree may have a slender trunk but it has branches. Branches have twigs and twigs have leaves. Branches, twigs and leaves are composed mostly of water. Water is heavy stuff. The weight of your tree canopy is going to be both heavier and larger than your pot. Now add the action of the wind. (Study Newton's laws of motion here.)
Before you know where you are, the force of the wind acts upon the mass of the tree canopy which in turn puts pressure on the trunk, the base of the trunk acts as a fulcrum on the contents of the pot (which are lighter than the canopy) and bingo! Newton's Law of Gravity is demonstrated.
In short, it won't be a great success in terms of plant cultivation.
But you may learn a bit about physics.
You explain it so well Pansyface - my reply was going to be more succinct and less interesting, but essentially reaching the same conclusion.
I can be hired for after dinner talks. Guaranteed to send the party to sleep.
Rather than a tree, how about trying bamboo. I was thinking about this to conceal a neighbours dilapidated shed which overlooks my kitchen window. In pots, the bamboo would also be restricted, yet you would still have height without the width of a tree.
A 50cm Pot is more suited to something 5-6 ft such as Acer Palmatum.
5-6 metres is not going to go well in a 50cm pot.