representing many unique categories that can grow

data class SpecialTypeContract(
        val value: BigDecimal,
        val excess: BigDecimal
)

data class CustomerContract(
        val name: String,
        val value: BigDecimal,
        val specialType:  SpecialTypeContract?,
        val itemContracts: List<ItemContract>
)

data class ItemContract(
        val name: String,
        val value: BigDecimal,
        val excess: BigDecimal
)


Category  |  options
TypeA  |  Special
TypeB  |  item and special
TypeC  |  item 
TypeD  |  item

In my application, I allow customers to purchase CustomerContract which can have a collection of ItemContract and/or SpecialTypeContract.

I support many categroies A...D and this can grow. For each of the categories I define whether they are available as SpecialTypeContract or as ItemContract.

For each of the above categories, there is a set of excess options to choose from i.e. 300, 800, 1000. The categories can also have rate/interest levels e.g. 0.1, 2.1 etc.

My question is, is there a design pattern I can use to represent this relationship between the categories and the contracts I have Special and Item ?

How should I represent these categories types A...D and provide what options they are available to customers? Should I use a data structure or some class hierarchy given that the list of types could grow later and have properties such as set of excess available and the rate/interest?