Having problem with scoring system.,

So, basically in my game player can plant trees and each fully grown tree will be counted +1 and +10 coins. There are 4 stages for the growth starting with seed until fully grown tree and the growth is one day one stage increase. So, the tree will be counted only when the tree is full grown. To achieve this I tried to assign the fully grown prefab with the tag of "pickup". The problem is, let say I planted 10 trees (seed) in the first batch and next after a day I planted 2 trees. When the first batch trees a fully grown, the tree will be counted 10 and coins 100. But when the next batch has fully grown then the game will display 22 trees (which is trees after first batch = 10, + the first batch number = 10 + 2 second batch trees). This means the game will continuously add all of the trees in a looping. How do I fix this?

For the scoring system, I have two script. First is ScoreManager and second is TreeScore.

This is the code inside my ScoreManager:

public class ScoreManager : MonoBehaviour
{
    public static ScoreManager instance;
    public int score = 0;
    public int tree = 0;
    public Text scoreText;
    public Text treeText;
    public Sprite spriteBlue;
    public Image spritered;
    private GameObject[] getCount;
    public int count;
    public string tag;

 void Start()
 {  
     scoreText.text = score.ToString();
     treeText.text = tree.ToString(); 
 }

 void Awake()
 {
     instance = this;
 }

 public void AddCoins()
 {
         score += 10;
         tree += 1;

         getCount = GameObject.FindGameObjectsWithTag("pickup");
         count = getCount.Length;

         scoreText.text = score.ToString();
         treeText.text = tree.ToString();
 }

}

And this is the calling method in my TreeScore:

ScoreManager.instance.AddCoins();

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