Drag and Drop

Below is a snapshot of whats happening and what im trying to accomplish. When i drag an item to the appropriate slot, it stays. However when I drag a different item on top of the one that's already there, I want it to go back to its original (sub)parent/start position. What's happening is that all objects are going to the same (sub) parent.

Im not sure where im going wrong in code. (beginner programmer)

So the question is, how do i get the "already" dragged item, to return to its original parent when i drag another item on top of it?

Thanks

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.EventSystems;
 
 public class DragHandler : MonoBehaviour, IBeginDragHandler, IDragHandler, IEndDragHandler {
 
 
     /// <summary>
     /// THIS HANDLES THE SELECTING AND DRAGGING OF THE OBJECT
     /// </summary>
 
 
     public static GameObject itemBeingDragged;
 
     Vector3 startPosition;
     Transform startParent;
 
     public static Transform originalStartParent;
 
     #region IBeginDragHandler implementation
 
     void Start()
     {
         originalStartParent = gameObject.transform.parent;
     }
 
     public void OnBeginDrag (PointerEventData eventData)
     {
         itemBeingDragged = gameObject;
         startPosition = transform.position;
         startParent = transform.parent;
         GetComponent<CanvasGroup> ().blocksRaycasts = false;
     }
 
     #endregion
 
 
 
 
     #region IDragHandler implementation
 
     public void OnDrag (PointerEventData eventData)
     {
         transform.position = Input.mousePosition;
     }
 
     #endregion
 
 
 
 
     #region IEndDragHandler implementation
 
     public void OnEndDrag (PointerEventData eventData)
     {
         itemBeingDragged = null;
         GetComponent<CanvasGroup> ().blocksRaycasts = true;
         if (transform.parent == startParent) 
         {
             transform.position = startPosition;
         }
     }
 
     #endregion
 
 
 
 }

 //------------------------------------------------------------------------------------------------------------------
 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.EventSystems;
 
 public class Slot : MonoBehaviour, IDropHandler {
 
 
     /// <summary>
     // THIS HANDLES WHICH SLOTS CAN GRAB THE ITEM 
     /// 
 
 
     public GameObject item
     {
         get
         {
             if (transform.childCount > 0) 
             {
                 return transform.GetChild (0).gameObject;
 
             }
             return null;
         }
 
      }
 
 
     #region IDropHandler implementation
     public void OnDrop (PointerEventData eventData)
     {
         if (!item)
             DragHandler.itemBeingDragged.transform.SetParent (transform);
         
         else if (item)
             item.transform.SetParent (DragHandler.originalStartParent);
             DragHandler.itemBeingDragged.transform.SetParent (transform);
 
 
     }
     #endregion
 
 
 }