Find closest transform

How do I find the closest transform of:

 public GameObject test;
 public Transform[] nodes;
 
     // Use this for initialization
     void Start () {
     
     }
     
     // Update is called once per frame
     void Update () {
         nodes = test.GetComponentsInChildren<Transform>();
         nodes [0] = nodes [nodes.Length - 1];
     
     }

like this