def get_value_map(self):
        """Obtain the value-to-class mapping set by user.

        :returns: The complete mapping as a dict of lists.
        :rtype: dict
        """
        value_map = {}
        tree_clone = self.tree_mapping_widget.invisibleRootItem().clone()
        for tree_branch in tree_clone.takeChildren():
            value_list = []
            for tree_leaf in tree_branch.takeChildren():
                value_list += [tree_leaf.data(0, Qt.UserRole)]
            if value_list:
                value_map[tree_branch.data(0, Qt.UserRole)] = value_list
        return value_map
Obtain the value-to-class mapping set by user.

        :returns: The complete mapping as a dict of lists.
        :rtype: dict