It would be super helpful to have a ticket add-on option. For example, in one of my events I have a group ticket for an educator attending our conference with a group of 5 students set at a certain cost. Those purchasing that ticket type have the option to purchase more student tickets a discounted price. As it is now, I have to list that additional student ticket in with all of the other tickets with a description that only those purchasing the group ticket are eligible. So I currently have to check over each ticket purchase and make sure that the discounted student ticket hasn't been added to an order without the group ticket.