Transform.root

説明

階層の一番上の Transform

（ Transform が親を持たない場合は自身を返すことになり、null が返ることはありません。）

	// Is a collision between two objects in different hierarchies?
	function OnCollisionEnter(collision : Collision) {
		if ( collision.transform.root != transform.root ) {
			print("The colliding objects are not in the same hierarchy");
		}
	}

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    void OnCollisionEnter(Collision collision) {
        if (collision.transform.root != transform.root)
            print("The colliding objects are not in the same hierarchy");
        
    }
}