Complexity

The structures of tech trees vary quite widely. In the simplest cases[citation needed] (e.g. Master of Orion) there are several completely separate research areas and one could research all the way up to the highest level in one area without researching other areas (although this would often be suicidal). In the most complex cases[citation needed] (e.g. Civilization) every technology above the starting level has more than one prerequisite and one has to research most of the lower-level technologies in order to research any of the top-level technologies. And there are many possibilities between these two extremes, for example in Space Empires researching to a specified level in one field may enable the player both to research to a higher level in that field and to start research in a new field which was previously not available.

Major 4X games like Civilization and Master of Orion have a much larger technology tree than most other strategy games; as an extreme example, Space Empires III has over 200 technologies