First, create a branch that holds the NMUs from the tip of your
debian-branch (default is master) once:
To import an NMU, change into the git repository and use gbp import-dsc:
This will import the NMU onto the branched named nmu
instead of the default
master. This method can also
be used to import "old" releases into the Git™ repository when migrating
to Git™ from another VCS.