I'm trying to make two partitions out of an 8 GB (4 GB each of course) USB drive using GParted and to create a bootable drive for Ubuntu 16.04 LTS in the first drive and Linux Mint 18 in the second drive. I succeeded in creating the partitions, but cannot select the partitions while making bootable drive using startup disk creator. It's showing as a single USB drive. So I decided to eject or unmount a drive to make a bootable drive in the other drive and then to the other. But two partitions are shown as parent drives and cannot be ejected separately. Anyone has a solution for this?
Edit: I'm trying to make bootable disk with the USB partitions for installing OS to a computer, not to boot the OS from the USB drive partitions.