It's the container that has to create and commit the transaction. You seem to believe that it should (a) know to and (b) know how to intercept the call made by the 'external' method (addAll) to the 'internal' method (add) to do this. So, the call sequence would be like: container -> addAll -> container -> add -> ...
I don't know if this is within the remit of an EJB container but it sounds to me like a non-trivial problem that it is best to avoid.
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