Re: How can I create a commit without a parent?

Ron Garret [off-list ref] writes:

git commit-tree insists on having at least one parent commit at 
the command line.

Incorrect.  "git commit" might but "git commit-tree" does.  Perhaps you
are forgetting that the first object name is a tree to be wrapped.

A short answer is that you don't create a root commit twice in a single
repository, period.  Your repository _may_ be end up with more than one
root but that typically is due to you fetching unrelated histories from
different repositories, each created its own root.