MainMenu.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.SceneManagement;

public class MainMenu : MonoBehaviour
{
    public int backmenu;

    public void LoadScene(int sceneIndex)
    {
        SceneManager.LoadScene(sceneIndex);
    }



    public void Exit()
    {
        Application.Quit();
    }

    protected virtual void Update()
    {
        if (Input.GetKeyDown(KeyCode.Escape) && SceneManager.GetActiveScene().buildIndex !=backmenu) LoadScene(backmenu);
    }
}