Shopify Product Creation Help

I am building a shopify product. And my item has 2 options, with 7 variants under each style.

Basically, the person selects, option 1 or option 2 and then the size of each has 7 options.

When I try and set this up with the 2 options, I input 14 variants total but it is not picking up that 7 are for the 2nd option. How do I designate which variants are for the 1st option vs the 2nd option?