Natural menthol is mainly (-)-Menthol. This is ONE of the 8 sereo-isomers of 2-isopropyl-5-methyl-cyclohexan-1-ol The stereo configuration can be labeled as (1R,2S,5R) for (-)-Menthol, the molecular formula is C10H20O.
Stereo-structures of Menthol are found in 'Related links' at the bottom of this answer page.