I bought a cherry tree (not the fruit kind) in a supermarket a few
months ago, and plonked it in my small yard against a fence by lifting a
couple of the block paving stones. It's not exactly shaded, but only
gets about three hours of direct sun a day.

It seems to have taken fine, with lots of leaves on the two 'side'
branches. The problem is the central branch which seems to have gone out
of control. It's just keeps reaching for the sky, and has probably grown
4 inches in the past week. There's lots of little branch and leaf
activity, but it's all hanging off a very spindly centre branch. I've
supported this centre branch by tying it to a bamboo cane, but now it's
gone beyond the 5 foot cane on its spindly ascent, and is lops over to
one side. The other branches are about 2 feet below the the tip, on a
tree that's about 6 feet high.

I looked on the RHS web site, and they seem to say 'don't prune the
centre branch'.

Any ideas please? I am so obviously not a gardener, but i've quite taken
to this creation of mine.

Thanks, Rob