This paper extends the multiparty asynchronous session types to symmetric sumtypes, which can
type non-deterministic orchestration choice behaviours. While the original branching in the session
types requires one participant to decide how to proceed by sending a label, with symmetric sumtypes
the choice can be made in a non-deterministic way by synchronisation between the participants in a
multiparty session. The motivation for synchronisation comes from natural and concise modelling
of social interaction and cooperation in healthcare scenarios in the Process Matrix. The behaviour of
synchronisation is represented by a new synchronise process constructor, which is typed by symmetric
sumtypes. Finally we show that symmetric sumtypes can be erased into the original branching
types with the help of conductor processes, preserving typability and operational semantics.