If you have two licences you could do it but I am not sure how boot would work. Why do you want 2x win 10 on same PC?
what type of bios have you got? Where both clean installs of win 10? The boot method would decide how easy it is. UEFI boot method might see both and offer a choice at start up everytime you boot, Legacy would just see whatever is first and wouldn't be usable if you have clean installed win 10 at any stage
you could use the msconfig boot tab to switch which to boot off.
I can't find any examples of it so I can't link them.