BSD and Linux

I am used to the fact that a Linux installer honours a pre-existing install of Windows and offers to setup the computer with a dual-boot option during installation. Vice-versa no Windows installer honours any other pre-exisiting OS. Therefore I was surprised that when I tried to install Ubuntu 16.04 on my PFSense box (FreeBSD), the Ubuntu installer did not even see that a BSD install exists on the drive. I chose the "erase all" option, but when I rebooted after the installer has finished, the system went straight into PFSense without giving me any option to select Ubuntu. I guess the boot loader had not been touched by the Ubuntu installer. I booted from a live Ubuntu USB stick, reformatted the drive with fdisk and wrote zeros to the boot loader:
dd if=/dev/zero of=/dev/sda bs=512 count=1
Then I repeated the install and everything was fine. However, my PFSense installation was lost...