how to embed?

[Collection("warehouse.transactions")]
public class Transaction
{
    public ObjectId id { get; set; } = ObjectId.GenerateNewId();
    [Required]
    public DateTime Time { get; set; } = DateTime.UtcNow;

    [Required]
    public double Amount { get; set; }

    [Required]
    public Item? Item { get; set; }

    [Required]
    public Warehouse? Warehouse { get; set; }

    [Required]
    public Buyer? Buyer { get; set; }

    [Required]
    public Staff? Staff { get; set; }
}