def METHOD_NAME():
    """Update PATH to include installed Multipass, if not already set."""
    assert sys.platform == "win32"
    key = winreg.OpenKey(winreg.HKEY_CURRENT_USER, "Environment")
    paths = os.environ["PATH"].split(";")
    # Drop empty placeholder for trailing comma, if present.
    if paths[-1] == "":
        del paths[-1]
    reg_user_path, _ = winreg.QueryValueEx(key, "Path")
    for path in reg_user_path.split(";"):
        if path not in paths and "Multipass" in path:
            paths.append(path)
    # Restore path with trailing comma.
    os.environ["PATH"] = ";".join(paths) + ";"