creates timetable context entry

def timetable_tree_entry(tree_name,
                         enclosed_processes,
                         dependent_on=None,
                         mx_name=None,
                         mx_page=None):
    """ creates timetable context entry """
    assert enclosed_processes is not None and not isinstance(enclosed_processes, string_types)
    assert dependent_on is not None and not isinstance(dependent_on, string_types)

    timetable_entry = TimetableTreeEntry(tree_name=tree_name,
                                         enclosed_processes=enclosed_processes,
                                         dependent_on=dependent_on,
                                         mx_name=mx_name,
                                         mx_page=mx_page)
    return timetable_entry