def combine_simulation_input(tree_list, p_dicts, rng_seeds=None):
    """Combine input for multiple simulations."""
    assert len(p_dicts) == len(tree_list
        ), 'Number of trees does not match the number of records with parameter values.'
    if rng_seeds is not None:
        assert len(p_dicts) <= len(rng_seeds), 'There must be at least ' + str(
            len(p_dicts)) + ' seed numbers.'
    assert len(p_dicts) > 0, 'No records to process!'
    rng_seeds = rng_seeds if rng_seeds else [None] * len(p_dicts)
    zipped = zip(tree_list, p_dicts, rng_seeds)
    return zipped
