Reference and populate object embedded

Working with Data
,
1

Hello,
I would like to create a reference between a document of a collection and one embedded subdocument of another collection
For example, this is the first collection

import mongoose from "mongoose";

const deviceSchema = new mongoose.Schema(
  {
    mac: {
      type: String,
      required: true,
    },
    unit: {
      type: mongoose.Schema.Types.ObjectId,
      ref: "sede", // but the reference should be to sede.room
    },
);

const Device = mongoose.model("device", dispoSchema, "device");

export default Dispo;

the second collection is

import mongoose from "mongoose";

const sedeSchema = new mongoose.Schema(
  {
    codifica: {
      type: String,
      required: true,
      unique: true,
    },
    room: [
        {
        code: {
          type: String,
        },
        place: {
          type: String,
  
        },
      },
    ],
  },
  { timestamps: true }
);

const Sede = mongoose.model("sede", sedeSchema, "sede");

export default Sede;

This is a simplified example document of the first collection

{
_id: ObjectId("abc123")
mac: "abcd11"
unit: ObjectId("123456")
}

This is a simplified document of the second collection

{
_id: ObjectId("xsd444")
codifica: "abceee21"
room: [
  {_id: ObjectId("123456"), code: "room1", place: "floor"},
  {_id: ObjectId("333333"), code: "room2", place: "ceil"},
]
}

I expect to populate all documents from the first collection to achieve this

[...
{
_id: ObjectId("abc123")
mac: "abcd11"
unit: { 
 id: ObjectId("123456"), 
 code: "room1", 
 place: "floor"
 }
},
...]

Thanks!!!