def node_scale_root_height(self, treeheight=<NUM_LIT:1>):
<EOL>ctree = self._ttree.copy()<EOL>_height = ctree.treenode.height<EOL>for node in ctree.treenode.traverse():<EOL><INDENT>node.dist = (node.dist / _height) * treeheight<EOL><DEDENT>ctree._coords.update()<EOL>return ctree<EOL>
Returns a toytree copy with all nodes scaled so that the root 
height equals the value entered for treeheight.