Please use code tags when posting code.
This is totally possible. If I had to guess, it would be because your field isn’t public and so not accessible outside of the class (c# defaults to private fields). I’m guessing you just typed that code in the forum editor because I’m pretty sure that’s not even compilable.
using UnityEngine;
using System.Collections;
[System.Serializable]
public class Container
{
[SerializeField]
public Container containerSub;
}