Or, for example:

Unit------Dark Knight------Death Knight------Champion of Darkness
Ability-------------------------Curse Strike------Zombie Strike
Ability---------------------------Dispel---------------Berserk

Unit----------Undead----------Harbinger of Death------Banshee
Ability-------Aura of Terror------Aura of Terror------Aura of Terror
Ability--------------------------Devastating Grasp------Piercing Wail
Ability----------------------------Unholy Word------Grief Strike
Ability------------------------------------------------------Fear Attack