How to merge objects in a document on update in Mongoose?

Question

MongoDB

Hi all. There is a document update task in MongoDB.
Suppose I have a document in the database that looks like this:

{
   "phone": "+7********",
   "profile: {
       "username": "Username",
    }
}

And from the client I receive an object:

{
   "profile": {
        "firstname": "My name"
    }
}

How to make it so that when updating the profile object is not overwritten, but objects are merged? For example, if there is no firstname parameter in the object, then it would simply be added, and if it exists, then it would be updated.
My code so far is this:

User.findOneAndUpdate(id, {$set: {profile: data.profile}}, {new: true}, (err, updatedUser) =>{
....
}