Ocasionally, you may want to keep branches in your repository that do not share an ancestor with your normal code. Some examples of this might be generated documentation or something along those lines. If you want to create a new branch head that does not use your current codebase as a parent, you can create an empty branch like this:
git symbolic-ref HEAD refs/heads/newbranch
rm .git/index
git clean -fdx
<do work>
git add your files
git commit -m 'Initial commit'