Dual Boot Windows 10 & Ubuntu Mate (or any flavor) on Dell Inspiron 5559

I bought a new DELL with with Windows 10 at Costco, and I want to dual boot with Ubuntu.

Unfortunately, though I've tried several different settings in the UEFI BIOS, and tried putting the boot loader in different places-I've even tried EasyBCD. But I still can't get the process down right. After installing Ubuntu, I either get "no operating system found" or I'm back to Windows 10 without a Ubuntu option.

I CAN boot Ubuntu from a flash drive using "shift & cntrl" when shutting down Windows 10, then choosing the "boot from a flash drive" option. For me, this is a last resort. I'd really like to be able to dual boot.

I'd appreciate some guidance.

Thanks!
David