Each Oxydendrum has a different shape, if you want a tall and narrow one you may need a different individual - some can be low and broad, just because of their genetics. If yours wants to grow that way it will be an uphill battle to try and make it into one that has a different structure.

The possible deleterious effects of cutting off the one stem depend on variables not conveyed here, such as how much of the total top it makes up and how big the specimen is now - you can do a lot more whacking on young and small, undeveloped trees than ones that are much farther along.

NEVER CUT A NEW TRANSPLANT ..

every leaf is a food making machine ...

plant it.. get it ESTABLISHED ... for a year or two ...

find out if its grafted ...

and if NOT .. then in a year or two.. you start training it into the form you want ...

if .. you cut off half of the food making machines.. its leaves.. what is going to feed the roots.. to get the plant firmly established??? prayer???

this tree could live 50 to 100 hundred years... there is never a hurry.. to prune...

and.. when the trunk is 6 to 12 inches thick.. it isnt going to matter... what it looks like today ... or next year..

think in tree years... not in terms of annuals/perennials ...

ken