[git] Why do I need to do `--set-upstream` all the time?

All i wanted was doing something like this:

git checkout -b my-branch
git commit -a -m "my commit"
git push

Since i didn't found a better solution, i've just created an bash alias on ~/.bashrc:

alias push="git push -u origin HEAD"

now just doing a push command does the job (you can add this alias on ~/.gitconfig too with another name, such as pushup)