/etc/grub.d/40_custom

#!/bin/sh
exec tail -n +3 $0
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change
# the 'exec tail' line above.

menuentry "Windows" {
 regexp -s root '\((.+)\)' "$cmdpath"
 chainloader /EFI/Microsoft/Boot/bootmgfw.efi
}