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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 dump_tree(self, statement=None, indent_level=0):
 """Dump the AST for this parsed file. Args: statement (SensorGraphStatement):
 the statement to print if this function is called recursively. indent_level (int):
 The number of spaces to indent this statement. Used for recursively printing blocks of statements. Returns: str: The AST for this parsed sg file as a nested tree with one node per line and blocks indented. """


        out = u""

        indent = u" "*indent_level

        if statement is None:
            for root_statement in self.statements:
                out += self.dump_tree(root_statement, indent_level)
        else:
            out += indent + str(statement) + u'\n'

            if len(statement.children) > 0:
                for child in statement.children:
                    out += self.dump_tree(child, indent_level=indent_level+4)

        return out