Create a pivot from selected GameObjects in unity

CreatePivotFromSelection.cs

using System.Collections.Generic;
using UnityEngine;
using UnityEditor;
using System.Linq;

public class CreatePivotFromSelection
{
    static void CreatePivot(Vector3 offset)
    {
        if (Selection.gameObjects == null || Selection.gameObjects.Length <= 0)
            return;

        var pivot = new GameObject();

        var bounds = new Bounds();
        foreach (var g in Selection.gameObjects)
        {
            var m = g.GetComponent<MeshFilter>();
            if (m)
            {
                var xform = g.transform;
                var bbox = new Bounds(xform.TransformPoint(m.sharedMesh.bounds.center), xform.TransformVector(m.sharedMesh.bounds.size));

                if (g == Selection.gameObjects[0])
                {
                    bounds = bbox;
                }
                else
                {
                    bounds.Encapsulate(bbox);
                }
            }
        }

        pivot.transform.position = bounds.center + new Vector3(bounds.size.x * offset.x, bounds.size.y * offset.y, bounds.size.z * offset.z);

        var movable = new List<GameObject>(Selection.gameObjects);

        foreach (var g in Selection.gameObjects)
        {
            if (g.transform.parent == null || g.transform.parent.parent == null)
            {
                var old = g.transform.parent;
                g.transform.parent = pivot.transform;

                movable.Remove(g);
                for (var i = 0; i < g.transform.childCount; ++i)
                {
                    var child = g.transform.GetChild(i);
                    if (Selection.gameObjects.Contains(child.gameObject))
                    {
                        movable.Remove(child.gameObject);
                    }
                    else
                    {
                        child.parent = old;
                    }
                }
            }
        }

        foreach (var g in movable)
        {
            g.transform.parent = pivot.transform;
        }
    }

    [MenuItem("GameObject/Create Ground Pivot from Selection", false, 11)]
    public static void CreateGroundPivot()
    {
        CreatePivot(new Vector3(0, -0.5f, 0));
    }

    [MenuItem("GameObject/Create Center Pivot from Selection", false, 12)]
    public static void CreateCenterPivot()
    {
        CreatePivot(new Vector3(0, 0, 0));
    }
}

amazing. love it. it works!