How can I instantiate a single prefab from an array?

I have a code that spawns obstacles in front of the player. It has an array of obstacle prefabs, and chooses 1 random obstacle from that array. I have made a count int into to the game that look how many prefabs can be instantiated. I also put a destroy with tag if the count is crossed. But now it just instantiates bunch of obstacles and deletes them "1 second" later.

 public class ObstacleSpawner : MonoBehaviour
 {
     //For the start of the game a swipe must be done
     private Vector2 swipeStartPos;
     private Vector2 swipeEndPos;
 
     //array for obstacleprefabs trees
     public GameObject[] trees;

     public bool mängAlgas = false;    //game began bool
     public bool round2 = false;
     public GameObject Player;    
     public int maximumObj;    
     public GameObject[] howManyTreesHaveBeenInstantiated;    
     public AudioSource mainTheme;        
     private int count = 0;
     public AudioSource jumpSound;          
     public GameObject surmaLaulja;
     public GameObject ScoreCounter;
 
     // Start is called before the first frame update
     void Start()    
     {
         surmaLaulja.SetActive(false);
 
         if (mängAlgas != true)
         {
             return;
         }
 
         else if (mängAlgas == true)
         {
             mainTheme.Play();
             StartCoroutine("SpawnDelay");
             //return;
         }            
     } 
     void Update()
     {
         SpawnDelay();
         howManyTreesHaveBeenInstantiated = GameObject.FindGameObjectsWithTag("Tree");
         count = howManyTreesHaveBeenInstantiated.Length;
         if (ScoreCounter.GetComponent<ScoreCounter>().mängLäbi == true)
         {
             surmaLaulja.SetActive(true); 
         }
 
 #if UNITY_EDITOR
        DetectMousePress(); 
        
        
 #else
        
        DetectTouchPress();
        
 #endif
         SwipeEnded();
     }
 
     private void SpawnTrees()
     {
         if (count <= 1)
         {
             print("I'm Spawning a tree.");
             
             float randomXValue = Random.Range(927f, 1500f);                       
             
             Vector2 spawnPos = new Vector2(randomXValue, 50f);
              
             Instantiate(PickRandomTree(), spawnPos, Quaternion.identity);                          
         }
         else if ( >= count)
         {
             Destroy(GameObject.FindGameObjectWithTag("Tree"));
         }
     }
     private GameObject PickRandomTree()
     {
         int randomNumber = Random.Range(0, trees.Length);
 
         GameObject treeThatWeChose = trees[randomNumber];
         return treeThatWeChose;
     }                
     public void DetectTouchPress()
     {
         foreach (Touch touch in Input.touches)
         {
             if (touch.phase == TouchPhase.Began)
             {
                 jumpSound.Play();
                 //start of the touch
                 print("Touch began at" + touch.position);
                 swipeStartPos = touch.position;
             }
             if (touch.phase == TouchPhase.Ended)
             {
                 print("touch ended at" + touch.position);
                 swipeEndPos = touch.position;          
                 
             }
            
         }
     }
 
 
     //Mouse down - Mouse Up record
     public void DetectMousePress()
     {
         //print("Detection Button Input");
         if (Input.GetMouseButton(0))
         {
             jumpSound.Play();
             //Start of the press
             //print("Mouse button was pressed at " + Input.mousePosition);
             swipeStartPos = Input.mousePosition;
         }
         if (Input.GetMouseButtonUp(0))
         {
             //End of the press
             //print("Mouse button was released" + Input.mousePosition);
             swipeEndPos = Input.mousePosition;
 
         }
      
     }
     public void SwipeEnded()
     {
         Vector2 swipeVector = swipeEndPos - swipeStartPos;
 
         if (Mathf.Abs(swipeVector.x) > Mathf.Abs(swipeVector.y))
         {
             //print("swipe was horizontal");
             if (swipeVector.x < 0f)
             {
                 //print("mäng algas");
                 mängAlgas = true;
                 Start();
             }       
         }
     }   
 }