Debian provides an archive with files for PXE boot network installation as explained here. The contents of the archive is meant be copied into an TFTP server's root directory and includes a pxelinux.cfg/default. With this setup, a PXE client will then offer a menu for Debian installation only.
I already have a PXE configuration for my TFTP server that provides various other boot options and would like to add the Debian netinstall as an additional option. I extracted the files from the archive into a subdirectory debian/stretch of the TFTP server. What do I have to put into pxelinux.cfg/default to forward to the Debian netinstall menu? Do I have to modify the Debian files to fit into the existing PXE setup?