Undo SetSiblingIndex for root objects?

I've created a script to naturally sort gameobjects by their name in the hierarchy, and I cannot seem to figure out how to use the built-in Undo system when root objects have SetSiblingIndex called on them.

Here's what I've got so far:

 using UnityEditor;
 using UnityEngine;
 using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.Text.RegularExpressions;
  
 namespace Zapdot
 {
     public static class EditorTools
     {
         [MenuItem("Tools/Utility/Sort Hierarchy #h", false)]
         public static void SortObjects()
         {
             List<Transform> objsToSort = new List<Transform>();
             Transform rootParent = null;
             int minIndex = int.MaxValue;
             if (Selection.transforms.Length > 1)
             {
                 rootParent = Selection.transforms[0].parent;
                 foreach (Transform t in Selection.transforms)
                 {
                     minIndex = Mathf.Min(minIndex, t.GetSiblingIndex());
                     objsToSort.Add(t);
                 }
                 if (rootParent != null)
                     Undo.RegisterCompleteObjectUndo(rootParent, "Sort Hierarchy");
                 else
                     Undo.RegisterCompleteObjectUndo(objsToSort.ToArray(), "Sort Hierarchy");
             }
             else if (Selection.activeTransform.childCount > 0)
             {
                 // since we're sorting all of the children, our minIndex would be 0.
                 minIndex = 0;
                 rootParent = Selection.activeTransform;
                 for (int i = 0; i < rootParent.childCount; ++i)
                     objsToSort.Add(rootParent.GetChild(i));
                 Undo.RegisterCompleteObjectUndo(rootParent, "Sort Hierarchy");
             }
  
             objsToSort.Sort(new NaturalNameComparer());
             for (int i = 0; i < objsToSort.Count; ++i)
                 objsToSort[i].SetSiblingIndex(minIndex + i);
         }
         [MenuItem("Tools/Utility/Sort Hierarchy #h", true)]
         public static bool SortObjectsValidate()
         {
             return Selection.transforms.Length > 1 || (Selection.transforms.Length == 1 && Selection.activeTransform.childCount > 1);
         }
     }
  
     public class NaturalNameComparer : IComparer<Transform>
     {
         private static readonly Regex _re = new Regex(@"(?<=\D)(?=\d)|(?<=\d)(?=\D)");
  
         public int Compare(Transform obj1, Transform obj2)
         {
             string x = obj1.name.ToLower();
             string y = obj2.name.ToLower();
             if (string.Compare(x, 0, y, 0, Mathf.Min(x.Length, y.Length)) == 0)
             {
                 if (x.Length == y.Length)
                     return 0;
                 return x.Length < y.Length ? -1 : 1;
             }
             var a = _re.Split(x);
             var b = _re.Split(y);
             int i = 0;
             while (true)
             {
                 int r = PartCompare(a[i], b[i]);
                 if (r != 0)
                     return r;
                 ++i;
             }
         }
  
         private static int PartCompare(string x, string y)
         {
             int a, b;
             if (int.TryParse(x, out a) && int.TryParse(y, out b))
                 return a.CompareTo(b);
             return x.CompareTo(y);
         }
     }
 }

To reproduce:

• Add this editor script to an empty project

• Create two gameobjects as root objects in a scene, "b" and "a"

• Select them both

• Run the function (shift h)

• Try to undo -- the objects don't reorder themselves to their original position.