Database
[{"Type":"CreditCard","Quarter":"20201","Expenses":[{"ExpenseType":"1","Amount":123},{"ExpenseType":"2","Amount":183}]},{"Type":"Cash","Quarter":"20202","Expenses":[{"ExpenseType":"1","Amount":345},{"ExpenseType":"2","Amount":200}]}]
Query
db.collection.aggregate({$group:{"_id":{"Quarter":"$Quarter","Type":"$Type"},"Total":{$push:{$reduce:{input:"$Expenses",initialValue:0,in:{$cond:[{$eq:["$$this.ExpenseType","1"]},{$add:["$$value","$$this.Amount"]},{$add:["$$value",0]}]}}}}}})