how save ValueObject on Mongodb with c#?

Question

public class PersianTitle : BaseValueObject<PersianTitle>
{

    public string Value { get; protected set; }
    protected PersianTitle()
    {
     
    }
    public PersianTitle(string value)
    {
        if (value.Length > 30)
        {
            throw new OutOfRangeException();
        }
      
        Value = value;
    }
    protected override IEnumerable<object> GetEqualityComponents()
    {
        yield return Value;
    }

}

public class Unit: Entity<string>
{
#region  Property

    public string UnitGroupId { get; private set; }
    public string Title { get; private set; }
    public PersianTitle Title2 { get; private set; }

}

{
  "UnitGroupId": "6447952a0f6108211573eb49",
  "Title": "u2984534589",
  "Title2": {
    "Value": "jkj"
  }
}

I want it saved like this without use Attribute on c#

{
  "UnitGroupId": "6447952a0f6108211573eb49",
  "Title": "u2984534589",
  "Title2": "jkj"
}