Extra brackets means extra dimensions.
A tensor with 1 dimension will be printed with 1 opening bracket, kind of like a list .
A tensor with 2 dimensions will be printed with 2 opening brackets, kind of like a list of lists .
A tensor with 4 dimensions will be printed with 4 opening brackets, kind of like a list of lists of lists of lists .
Like in the movie Inception they go 4 levels deep, so we see them start the dream machine 4 times.