As I mentioned in the beginning, this is a mod that adds a separate troop tree for each faction. However, the reason for this is that I don't want to change the game's balance a lot. This is a save-compatible mod that works on versions of the game that don't support mods. The new trees are as follows:

Empire - Clibanarii

A variant of cataphract, actually a synonym of "cataphract" during some period in real world.

Aserai - Noble Skirmisher

Fast, light armored mounted Skirmishers with 10 shots of javelins.

Vlandian - Mercenary Knight

Not every knight can have his own fief and peasants, some knights are forced to fight as Mercenaries, more skillful and more capable in more complex situations (they may bring two-hand weapons) but may spawned with cheaper armor.

Khuzait - Khheshig Lancer

A lancer variant of kheshig and khan's guard, with better armor capable for melee combat.