problem with item stacking

hello

i display a text list of the inventory. the problem is the stacking. sometimes it works sometimes it adds 2 to quantity. short: it dont work. i have a database with 3 items (id 0, 1, 2). here is the inventory script. the question is with the addItem function:

 public class Inventory : MonoBehaviour 
 {
     public List<Item> inventory = new List<Item>();
 
     private ItemDatabase database;
 
     public Transform parent;
 
     public GameObject itemEntry;
 
     public float maxWeight;
 
     void Start()
     {
         database = GameObject.FindGameObjectWithTag("Item Database").GetComponent<ItemDatabase>();
 
     }
     
     public void DrawInventory()
     {
         for(int i = 0; i < inventory.Count; i++)
         {
             Text itemQuantity;
             Text itemName;
 
             GameObject newItem = Instantiate(itemEntry) as GameObject;
                 
             itemQuantity = newItem.transform.FindChild("quantity").GetComponent<Text>();
             itemName = newItem.transform.FindChild("name").GetComponent<Text>();
                 
             newItem.name = parent.name + i;
             newItem.transform.SetParent(parent.transform,false);
                 
             //itemQuantity.text = inventory[i].itemQuantity;
             itemName.text = inventory[i].itemName;
             itemQuantity.text = "x " + inventory[i].itemQuantity;
         }
     }
 
     public void HideInventory()
     {
         var children = new List<GameObject>();
         foreach (Transform child in parent) children.Add(child.gameObject);
         children.ForEach(child => Destroy(child));
 
     }
     
     public void addItem(int id)
     {
         if(inventory.Count <= 0)
         {
             inventory.Add(database.items[id]);
         }
         else if(inventory.Count > 0)
         {
             for(int i = 0; 0 < inventory.Count; i++)
             {
                 if(inventory[i].itemID == id)
                 {
                     inventory[i].itemQuantity++;
                 }
                 else 
                 {
                     inventory.Add(database.items[id]);
                     break;
                 }
             }
 
         }
     }
 }
 

can someone help me? greets michi