[{myList:[[1,2],[1,3],]}]

db.collection.aggregate([{$project:{isUnique:{$cond:[{$in:[{$size:"$myList"},[0,1]]},true,{$ne:[{$reduce:{input:"$myList",initialValue:{$arrayElemAt:["$myList",0]},in:{$cond:{if:{$setEquals:["$$value","$$this"]},then:"$$value",else:[]}}}},[]]}]}}}])