(lowerdir) /chroot in /merged
(lowerdir) /home   in /merged/home
(upperdir) /tmpfs  in /merged

mount -t overlay -o lowerdir=/chroot:/home,upperdir=/tmpfs,workdir=/workdir overlay /merged
ls /merged

mount --bind /home /chroot/home
mount -t overlay -o lowerdir=/chroot,upperdir=/tmpfs,workdir=/workdir overlay /merged
ls /merged/home