$ mysql -uroot -Dtreect2 -p -e "SET AUTOCOMMIT=1; source bashtransaction.sql;"
Enter password: 
ERROR 1062 (23000) at line 2 in file: 'bashtransaction.sql': Duplicate entry '1' for key 'uq_tree_header'

DROP DATABASE IF EXISTS `treect2`;
CREATE SCHEMA `treect2` DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci;

USE `treect2`;

DROP TABLE IF EXISTS `treerel`;
DROP TABLE IF EXISTS `tree`;
CREATE TABLE IF NOT EXISTS `tree` (
  `id` INT unsigned NOT NULL AUTO_INCREMENT,
  `pid` INT unsigned NULL DEFAULT NULL,
  `header` VARCHAR(180) NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `uq_tree_header` (`header` ASC)
)
ENGINE InnoDB
AUTO_INCREMENT 1
DEFAULT CHARACTER SET utf8
COLLATE utf8_general_ci;

ALTER TABLE `tree`
  ADD CONSTRAINT `fk_tree_pid` FOREIGN KEY (`pid`) REFERENCES `tree` (`id`) ON UPDATE CASCADE ON DELETE RESTRICT;

CREATE TABLE IF NOT EXISTS `treerel` (
  `aid` INT unsigned NOT NULL,
  `did` INT unsigned NOT NULL,
  -- `level` INT unsigned NOT NULL,
  UNIQUE KEY `uq_treerel_adid` (`aid` ASC, `did` ASC),
  CONSTRAINT `fk_treerel_aid` FOREIGN KEY (`aid`) REFERENCES `tree` (`id`) ON UPDATE CASCADE ON DELETE RESTRICT,
  CONSTRAINT `fk_treerel_did` FOREIGN KEY (`did`) REFERENCES `tree` (`id`) ON UPDATE CASCADE ON DELETE RESTRICT
)
ENGINE InnoDB
DEFAULT CHARACTER SET utf8
COLLATE utf8_general_ci;

DROP TRIGGER IF EXISTS `tai_tree`;
DROP TRIGGER IF EXISTS `tbd_tree`;
DROP TRIGGER IF EXISTS `tbu_tree`;

CREATE TRIGGER `tai_tree` AFTER INSERT ON `tree` FOR EACH ROW
trigger_label:BEGIN
	IF @disable_triggers IS NULL THEN
		-- Если вставляем элемент в корень, то связи не добавляем
		IF NEW.`pid` IS NULL THEN
			LEAVE trigger_label;
		END IF;
		-- Вставляем связи
		INSERT INTO `treerel` (`aid`, `did`)
			-- Выбираем предков указанного родителя (did = idРодителя)
			-- и вставляем записи типа: idПредка, нашId
			SELECT `aid`, NEW.`id`
			FROM `treerel`
		    WHERE `did` = NEW.`pid`
			-- Родитель тоже предок
		    UNION ALL
		    SELECT NEW.`pid`, NEW.`id`;
	END IF;
END;

INSERT INTO `tree` (`pid`, `header`) VALUES (null, '1');
INSERT INTO `tree` (`pid`, `header`) VALUES (1, '1'); -- Тот самый инсерт с ошибкой
INSERT INTO `tree` (`pid`, `header`) VALUES (null, '2');

mysql -uroot -Dtreect2 -p -e "START TRANSACTION; source bashtransaction.sql; COMMIT;"