public void OnMouseDown()
{
if (upgradeMenuPrefab != null)
{
GameObject go = Instantiate <GameObject>(upgradeMenuPrefab);
UpgradeMenu upgradeMenu = go.GetComponentInChildren <UpgradeMenu>();
upgradeMenu.Initiate(this);
upgradeMenu.transform.position = Camera.main.WorldToScreenPoint(transform.position);
}
}