Testing.cs

using UnityEngine;
using System;
using System.Collections;
using System.Collections.Generic;

interface INode{  }
 
[Serializable]
class RootNode : INode
{
   [SerializeReference] public INode left;
   [SerializeReference] public INode right;
}
 
[Serializable]
class SubNode : RootNode
{
   [SerializeReference] INode parent;
}
 
[Serializable]
class LeafNode : INode
{
   [SerializeReference] public INode parent;
}
 
 [CreateAssetMenu()]
class Testing : ScriptableObject
{
    [SerializeReference]
    public List<RootNode>  m_Trees;
}