How can I save multiple relations 1:N in cascade on Laravel?

E.g this is a brief of my database:

bills
 -id
 -name

items
  -id
  -name
  -bill_id

item_members
  -id
  -user_id
  -item_id

For saving all items of a bill you can do: $bill->items()->saveMany($items). But how can I save all the item_members of item in cascade? like: $bill->items()->saveMany($items)->saveMany($item_members)?