Step-1 : General tab

In this case, you  will have to choose "Dependent product based discount" as discount method.

Step-2: Condition tab
 
In this example,  we are going to offer 50% discount for headphone if you buy Laptop. So choose,
Product(s) from - Laptop
get discount in - Headphone

Step-3: Discount tab
 
Enter the discount value 50 in percentage and save the rule.

Step-4: Frontend demo

Did this answer your question?