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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def create_treeitem(self, ):
 """Create a new treeitem for this reftrack instance. .. Note:: Parent should be set, Parent should already have a treeitem. If there is no parent, the root tree item is used as parent for the treeitem. :returns: a new treeitem that contains a itemdata with the reftrack instanec. :rtype: :class:`TreeItem` :raises: None """

        p = self.get_parent()
        root = self.get_root()
        if p:
            pitem = p.get_treeitem()
        else:
            pitem = root.get_rootitem()
        idata = root.create_itemdata(self)
        item = TreeItem(idata, parent=pitem)
        return item