Why is 1,1,2-trimethylpropane not an isomer of hexane

I know this is weird but I wrote this an answer to a question about isomers of hexane and I can't explain why it's wrong. I've checked online for an explanation but I haven't been satisfied with what I've found

I appreciate all help

1,1,2-trimethylpropane is the same as 2,3-dimethylbutane but named not-quite-correctly

As the user above posted, your molecule is not named correctly. Remember to use the longest chain when naming the molecule.

There are five isomers of C6H14.
https://en.wikipedia.org/wiki/C6H14
https://en.wikipedia.org/wiki/Hexane
https://byjus.com/question-answer/name-the-5-different-structural-isomers-of-hexane/
https://socratic.org/questions/what-are-5-different-structural-isomers-of-hexane