Mongodb 如何从同一集合中查询和获取组合结果

Im在mongodb（加密交换数据）中有一组代码，每秒钟我都会得到一条新记录

interface Ticker {
 base: Base;
 sec: Quoted;
 exchange: Exchange;
 volume24h?: number;
 open24h?: number;
 low24h?: number;
 high24?: number;
 change24h?: number;
 lastTrade?: number;
}

示例如下所示：

{
  base: "BTC"
  sec: "USD"
  exchange: "Liquid"
  volume24h: "20000"
  open24h: 10000
  low24h: 9800
  high24: 11000
  change24h: 3
  lastTrade: 9898
  createdAt: '2020-02-10T10:10:00'

}

我想得到的结果是一个数组，但我只想得到每个交换的最新记录（基于createAt日期）：

[
 btcusd: [
 {
  base: "BTC"
  sec: "USD"
  exchange: "Liquid"
  volume24h: "20000"
  open24h: 10000
  low24h: 9800
  high24: 11000
  change24h: 3
  lastTrade: 9898
  createdAt: '2020-02-10T10:10:00'
 }
],
 btcjpy: [
 {
  base: "BTC"
  sec: "JPY"
  exchange: "Binance"
  volume24h: "20000"
  open24h: 10000
  low24h: 9800
  high24: 11000
  change24h: 3
  lastTrade: 9898
  createdAt: '2020-02-10T10:10:00'
 }
],
 btcusdt: [],
]