5E Subraces

Looking for a little clarification on how subraces are created now. When creating a subrace using the new button on the race menu, you enter the parent race in a specific field. I am wanting to know if multiple races can be set as the parent race (the way spells have multiple class associations)?

Basically, I adding in the human ethnicities for Faerun and want them to be subraces (for starting languages and historical background info). If it is possible, I would like to only make one subrace and have it connected to the normal Human race and the Human Variant race.

EDIT: Separating by comma or semicolon does not work.

Pretty sure the answer is no. I've never tried, but given my understanding of the data architecture, it wouldn't be possible. In short, I would not spend further time trying unless someone says it is possible.

No, subraces can only belong to one race.

Regards,
JPG