Database

[{Name:"Name1",Product:1012,Titles:[{Id:5,Title:"FirstTitle"},{Id:75,Title:"SecondTitle"}]},{Name:"Name1",Product:2014,Titles:[{Id:5,Title:"FirstTitle"},{Id:75,Title:"SecondTitle"}]}]

Query

db.collection.aggregate([{$group:{_id:"$Name",Titles:{$addToSet:"$Titles"},original:{$push:"$Titles"}}},{$project:{Titles:{$cond:[{$or:[{$ne:[{$size:"$Titles"},{$size:"$original"}]},{$eq:[{$size:"$original"},1]}]},"$Titles",null]},TitlesVaries:{$ne:[{$size:"$Titles"},{$size:"$original"}]}}}])

Result