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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 copy(self):
 """Copy the this node tree Note all references to readers are removed. This is meant to avoid tree copies accessing readers that would return incompatible (Area) data. Theoretically it should be possible for tree copies to request compositor or modifier information as long as they don't depend on any datasets not already existing in the dependency tree. """

        new_tree = DependencyTree({}, self.compositors, self.modifiers)
        for c in self.children:
            c = c.copy(node_cache=new_tree._all_nodes)
            new_tree.add_child(new_tree, c)
        return new_tree