[{_id:"SG",count:76},{_id:"IN",count:6},{_id:"US",count:4},{_id:"FR",count:3},{_id:"UK",count:2},{_id:"RU",count:1},{_id:"CO",count:1},{_id:"DK",count:1},{_id:"ID",count:1},{_id:"PH",count:1}]

db.collection.aggregate([{$group:{_id:null,roots:{$push:"$$ROOT"},sum:{$sum:"$count"}}},{$addFields:{roots:{"$concatArrays":["$roots",[{_id:null,count:"$sum"}]]}}},{$unwind:"$roots"},{$replaceRoot:{newRoot:"$roots"}}])