How to use "Build collection activity"?

I want to built a collection
How to use “Build collection activity”??

it shows me an error , I put CollectionB in next item field


Can you try as the following?

First, set single item at First item property.
Next, set remaining items at Next items property.
Finally, set List<T> type variable at New Collection property. This type seems to be determined from type of first item. (And output type should be set not ICollection<T> but List<T>