According to Trek's Archives website, there are major differences in the two model years (2015 and 2006), which should make identification pretty quick and easy:

2015: 2x10 Tiagra, carbon fork blades, standard spoke wheels
2006: 3x9 Deore, alloy fork blades, paired-spoke wheels

Of course, there are many years in between as well. Do you know the components of the subject bike? That will help a lot.