How do you explain the presence of all the six carbon atoms in glucose in a straight chain?

When glucose is heated with $HI$ for a long time,it undergoes reduction to form $n$-hexane.
This reaction confirms that all six carbon atoms in glucose are linked in a straight chain.
The reaction is as follows:
$CHO-(CHOH)_4-CH_2OH \xrightarrow{HI, \Delta} CH_3-CH_2-CH_2-CH_2-CH_2-CH_3$ ($n$-Hexane)