If you want to add any product(free gift product) when any product added in cart then we must have to do customization.
i can give you way if you can.
1. you have to code for cart page so that if you get any specific product in cart you have to add your gift product in cart by Js code.
take one variable and and check condition in cart.item loop if you found you product in cart then trigger Js code to add gift product.
If you want me to do that Pm me