[dmd-internals] Git question: How do I push a *single* branch?

[Don Clugston]

In my local repository I have two branches, branch1 and branch2.
I publish branch1 to github:
git push origin : branch1
A side-effect of this, is that it automatically makes branch1 a remote
tracking branch.

Now, I add an extra commit to branch1, but I don't want to push it yet.
But I do want to push branch2.
So I type:  git push origin : branch2
This creates branch2, BUT it also pushes branch1 as well!
How do I stop this?

 I can't see anything in the manual for git push that explains this.
How can I push branch2 *only* ?