Technology tree

In strategy computer games, the technology tree or tech tree is a hierarchical visual representation of the possible sequences of upgrades a player can take, most often through the act of research. The diagram is tree-shaped in the sense that it branches between each 'level', allowing the player to choose one sequence or another. Each level is called a tier and is often used to describe the technological strength of a player. Typically, at the beginning of a session of a strategy game, a player will start at tier 1, and will only have a few options for technologies to research. Each technology that a player researches will open up one or more new options, but may or may not, depending on the computer game, close off the paths to other options. The tech tree is the representation of all possible paths of research a player can take, up to the culmination of said sequence.