Selection.GetTransforms  

static function GetTransforms (mode : SelectionMode) : Transform[]

Description

Allows for fine grained control of the selection type using the SelectionMode bitmask.

// C# Example
// Creates a new parent for the selected transforms

using UnityEngine;
using UnityEditor;

public class CreateParentForTransforms : ScriptableObject {
    [MenuItem ("Example/Create Parent For Selection _p")]
    static void MenuInsertParent() {
        Transform[] selection =  Selection.GetTransforms(
        SelectionMode.TopLevel | SelectionMode.Editable);
        GameObject newParent = new GameObject("Parent");

        foreach(Transform t in selection)
            t.parent = newParent.transform;
    }
    // Disable the menu if there is nothing selected
    [MenuItem ("Example/Create Parent For Selection _p", true)]
    static bool ValidateSelection() {
        return    Selection.activeGameObject != null;
    }
}