function OnGUI() {
    if (GUILayout.Button ("Disconnect")) {
        Network.Disconnect();
        MasterServer.UnregisterHost();
    }
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void OnGUI() {
        if (GUILayout.Button("Disconnect")) {
            Network.Disconnect();
            MasterServer.UnregisterHost();
        }
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def OnGUI():
        if GUILayout.Button('Disconnect'):
            Network.Disconnect()
            MasterServer.UnregisterHost()