Iris Cohen wrote:

I planted a apple seed about 6 months ago, and I have a little tree now.
It's about a foot and a half tall. I have it in a pot on a window sill right
now. However the only growth on the tree is up. It is not branching out at
all, just some leaves on the trunk of the tree. Is this normal?

Yes, for a first year seedling. What are you planning to do with the tree?
Remember, it may not give fruit that is worth anything.

Ah, but they're like a fireworks show when they're in bloom, fruit or not.

First year trees regardless of type will look like twigs. You won't see a
real crown until about the fourth year.