[{"teams":[{"employees":[{"name":"john"},{"name":"david"}]},{"employees":[{"name":"oliver"},{"name":"sam"}]}]},{"teams":[{"employees":[{"name":"singh"},{"name":"jane"}]},{"employees":[{"name":"marleen"},{"name":"florence"}]}]}]

db.collection.aggregate([{$unwind:"$teams"},{$unwind:"$teams.employees"},{$replaceRoot:{newRoot:"$teams.employees"}}])