LINQ query to push an item to the array of a Mongo Document

I want to push a ProductPhoto inside the Product using LINQ. Here is my model:

public class Product
{
   public string Id { get; set; }
   public string Name { get; set; }
   public string Detail { get; set; }
   public List<ProductPhoto> ProductPhotos { get; set; }
}

public class ProductPhoto
{
   public string Id { get; set; }
   public string Url { get; set; }
}

How can I achieve this with the LINQ query? I am expecting the result to be something like this.

{
    _id: ObjectId('602d2149e773f2a3990b47f5'),
    Name: 'Some name',
    Detail: 'Some description',
    ProductPhotos: [
      { _id: ObjectId('602d2149e773f2a3990b47f5'), Url: 'Some URL' }
    ] 
}

Next time when I add a new ProductPhoto, then there will be two elements.

Thanks!