Timer reset

Hey guys, I have a timer in my game which should count the time till the end of the game.
I can’t figure out how to make it so it will only reset back to 0 when menu scene is active. ( build index 0)
The second problem is that I don’t want it to go back to 0 after every death(scene reload).
Have you got any sugestions?

using UnityEngine;
using UnityEngine.UI;
using UnityEngine.SceneManagement;

public class Timer : MonoBehaviour
public Text TimerText;
public bool shouldCountTime;
public float t;

private void Start()
	if (SceneManager.GetActiveScene().buildIndex != 0)
		shouldCountTime = true;
		shouldCountTime = false;
		t = 0;
	t = Time.deltaTime;

void Update()
	if (shouldCountTime) {
		t += Time.deltaTime;
	string minutes = ((int)t / 60).ToString();
	string seconds = (t % 60).ToString("f2");
	TimerText.text = minutes + ":" + seconds;


What I can suggest here would be to use a static float so it will stay in memory even when reloading a scene (and its script).