AddParent

using UnityEngine;
using UnityEditor;
using System.Collections;

public class AddParent : ScriptableObject
{
    [MenuItem ("GameObject/+Add Parent")]
    static void MenuInsertParent()
    {
        Transform[] transforms = Selection.GetTransforms(SelectionMode.TopLevel |
            SelectionMode.OnlyUserModifiable);

        GameObject newParent = new GameObject("_Parent");
        Transform newParentTransform = newParent.transform;

        if(transforms.Length == )
        {
            Transform originalParent = transforms[].parent;
            transforms[].parent = newParentTransform;
            if(originalParent)
                newParentTransform.parent = originalParent;
        }
        else
        {
            foreach(Transform transform in transforms)
                transform.parent = newParentTransform;
        }
    }
}