func Level1(c echo.Context) error {

    level1 := c.Param("level1")

    return c.String(http.StatusOK, level1)

}

func Level2(c echo.Context) error {

    level1 := c.Param("level1")

    level2 := c.Param("level2")

    return c.String(http.StatusOK, level1+"/"+level2)

}

    e.GET("test/v1/list/:level1", Level1)

    e.GET("test/v1/list/:level1/:level2", Level2)

$ curl http://127.0.0.1/test/v1/list/15
15

$ curl http://127.0.0.1/test/v1/list/15/18
15/18