Deep copy of a NaryTree

public class BehaviorTree {
  private BehaviorTreeNode root;
  public BehaviorTree() {
    root = new BehaviorTreeNode();
  }
  public BehaviorTree(BehaviorTree other) {
    // Implementation goes here
  }
}

public abstract class BehaviorTreeNodeBase
{
    protected static int ID;
    protected int _id;
    public BehaviorTreeNodeBase firstChildNode;
    public BehaviorTreeNodeBase siblingNode;

    public virtual BehaviorTreeState EvaluateNode(IBehaviorTreeAgent instance) { return BehaviorTreeState.None; }
    public abstract void AddNode(BehaviorTreeNodeBase other);

    public abstract void RemoveNode(BehaviorTreeNodeBase other);

    public int id
    {
        get { return _id; }
    }
}

public class BehaviorTreeNode : BehaviorTreeNodeBase
{
    public BehaviorTreeNode() {
        _id = ID;
        ID++;
    }

    public BehaviorTreeNode(BehaviorTreeNode other)
    {
        this._id = other._id;
    }

    public override void AddNode(BehaviorTreeNodeBase other)
    {
        //Add child node
    }

    public override void RemoveNode(BehaviorTreeNodeBase other)
    {
        //Remove child node
    }
}