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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 node_scale_root_height(self, treeheight=1):
 """ Returns a toytree copy with all nodes scaled so that the root height equals the value entered for treeheight. """

        # make tree height = 1 * treeheight
        ctree = self._ttree.copy()
        _height = ctree.treenode.height
        for node in ctree.treenode.traverse():
            node.dist = (node.dist / _height) * treeheight
        ctree._coords.update()
        return ctree