def METHOD_NAME(self, rootpath):
    if os.path.exists(os.path.join(rootpath,'trees')):
        return rootpath
    elif os.path.exists(os.path.join(rootpath, 'halos', 'trees')):
        return os.path.join(rootpath, 'halos')
    else:
        raise OSError("Cannot find the consistent-trees output")