Apple has updated Book Camp with support for Microsoft Windows 10. that lets it install Microsoft Windows 10.
You need support software (drivers) installed with Boot Camp to use Windows 10. This software is automatically downloaded when you use Boot Camp Assistant. Boot Camp supports 64-bit versions of Windows 10 when used with a supported Mac.
Windows 10 is available from Microsoft as an ISO file, an installation DVD, and a USB flash drive. You need an ISO file of the 64-bit version of the Windows 10 installer to install Windows on your Mac.
If you don’t have an ISO file, you can use Disk Utility to make one from your Windows installation DVD or USB flash drive. If you’re installing Windows for the first time, make sure the Windows installer you’re using is for a full installation (not an upgrade installer).