// First, we start a transaction and save it into a variable
const t = await sequelize.transaction();

try {

  // Then, we do some calls passing this transaction as an option:

  const user = await User.create({
    firstName: 'Bart',
    lastName: 'Simpson'
  }, { transaction: t });

  await user.addSibling({
    firstName: 'Lisa',
    lastName: 'Simpson'
  }, { transaction: t });

  // If the execution reaches this line, no errors were thrown.
  // We commit the transaction.
  await t.commit();

} catch (error) {

  // If the execution reaches this line, an error was thrown.
  // We rollback the transaction.
  await t.rollback();

}