The second, more advanced troops available to be recruited from towns. In order to recruit these troops, you must have some nobility which means either you join a faction or be your own faction's leader. Then you can recruit these troops from a friendly town.
The noble troop tree has more powerful and advanced troops that are tied with nobility (Swadian Knight is here for example) and is completely seperate from the regular troops. Their levels range from 25-50 and as such, these soldiers are expensive, hard to train but in return are very powerful whem trained to max, and will make most of the soldiers for a really powerful army since the third troop tree's units are really rare and hard to come by.