DB Accouns with tree dependency

CREATE TABLE IF NOT EXISTS users(
                     id         INT         NOT NULL AUTO_INCREMENT,
                     parent_id  INT         DEFAULT NULL,
                     password   VARCHAR(64) NOT NULL,
                     email      VARCHAR(60) NOT NULL,
                     registered TIMESTAMP   NULL DEFAULT CURRENT_TIMESTAMP,
                     PRIMARY KEY (id),
                     UNIQUE INDEX id_UNIQUE (id),
                     UNIQUE INDEX email_UNIQUE(email)
                 ),
                 ENGINE = INNODB,
                 AUTO_INCREMENT = 15,
                 AVG_ROW_LENGTH = 5461,
                 CHARACTER SET utf8mb4,
                 COLLATE utf8mb4_0900_ai_ci