C# adding items to List

I am trying to add items to a list using for the following;

public class Reason
{
    [JsonProperty("code")]
    public int Code { get; internal set; }
}

public class Item
{
    [JsonProperty("Id")]
    public int Id { get; set; }

    [JsonProperty("quantity")]
    public int quantity { get; set; }

    [JsonProperty("reason")]
    public Reason reason { get; set; } = new Reason();
}

public class RootObject
{
    [JsonProperty("dropOff")]
    public DropOff dropOff { get; set; } = new DropOff();

    [JsonProperty("providerId")]
    public int providerId { get; set; }

    [JsonProperty("orderReference")]
    public string orderReference { get; set; }

    [JsonProperty("returnMethodId")]
    public int returnMethodId { get; set; }

    [JsonProperty("items")]
    public List<Item> items { get; set; } = new List<Item>();
}


root.items.Add(new Item { Id = 8675072, quantity = 1, Reason.Code = 2  });

I am getting the following error when i am trying to add the Reason.Code,

An Object Reference is required for the non-field, method or property.

Where would i need to initialise to add Reason.Code to the list?