Sqlserver Trigger a quick look

This article demonstrates the #1 failure when people write triggers.
When writing SQL triggers you can NEVER be sure that you will ONLY have one record when processing the trigger results.
In Your example only the first record from the INSERTED table will be captured, or worse random bits through out will be logged as a single record.

Insert into Usertable ([name])
Values ('Bob'),
       ('Luke'),
       ('Frank'),
       ('James');

Your trigger would only capture Bob.
In order to fix this you need to write a cursor, or a CTE, or in this case your not actually performing any real work, you can do this.

INSERT INTO [TestDb].[dbo].[tt]
SELECT
 [ID],
 [Name],
 'Inserted Record -- After Insert'
FROM INSERTED

This actually simplifies your example as it doesn't require numerous variables to store values.