Dialogue Trees in Video Games

In the last decade one of the greatest developments I've seen in video game writing is the use of dialogue trees. A dialogue tree allows the player to respond to a NPC (non-player character) in nearly any way they would want. For example, your character approaches an NPC who seems angry. Your character will have a number of ways to respond to said NPC, from politeness to violence, or in between. These dialogue trees are most commonly seen in American RPGs, role playing games, such as Fallout 3 and Knights of the Old Republic. What really makes these dialogue trees interesting is when the way your character acts actually influences how other NPCs react to you. This not only makes dialogue trees fun, but it also allows customization into your character's personality.