When setting gift rules, you can enable the Multifold Gift icon to achieve Buy More Give More!

Steps
Step 1: Go to setting > Order Settings >Gift Rules > Add New Rule



Step 2: Select Designated Merchant SKU > select Buy More Give More > set merchant SKU(s)


set the gift products and qty > select the Multifold Gift




For example:  
Buy SKU A Get SKU B
2 1
4 2
5 2
7 3
 
Buy SKU A Get SKU B
2 1
4 1
5 1
7 1