as waterfall- and bubble-charts differ from each other, it really could make sense to split those into two different entities. You could create an entity “Chart” that holds all basic information and two entities that inherit from “Chart” (the generalization option). This would also increase the readability of your domain model.
I would also recommend to clean up your existing domain model. E. g. having the title in an extra entity doesn’t make any sense, as following the association is just one more step when looking up the title of a chart and it would be faster if the title was an attribute of the chart entity.