Unity C# Ładowanie wielu scen

using UnityEngine;
using UnityEngine.SceneManagement;
public class LevelManagerPi : MonoBehaviour
{

    void Start()
    {
        SceneManager.LoadScene("a", LoadSceneMode.Additive);
    }


    void Update()
    {
        if (Input.GetButtonDown("Fire2"))
        {
            SceneManager.UnloadSceneAsync("a");
        }
    }
}

using System;
using UnityEngine;
using UnityEngine.SceneManagement;

public class GameManager : MonoBehaviour
{
    public static GameManager Instance { get; private set; }
    public static Action OnSceneLoad;

    private void Awake()
    {
        if (Instance != null && Instance != this)
        {
            Destroy(this);
        }
        else
        {
            Instance = this;
        }
    }

    int activeSceneNumber = 0;
    int scenesTotal;
    void Start()
    {
        scenesTotal = SceneManager.sceneCountInBuildSettings;
        SceneManager.LoadScene(activeSceneNumber.ToString(), LoadSceneMode.Additive);
    }

    public void SwitchScene()
    {
        SceneManager.UnloadSceneAsync(activeSceneNumber.ToString());
        if (activeSceneNumber + 2 < scenesTotal)
        {
            activeSceneNumber++;
        }
        else
        {
            activeSceneNumber = 0;
        }
        SceneManager.LoadScene(activeSceneNumber.ToString(), LoadSceneMode.Additive);
        OnSceneLoad?.Invoke();
    }
}