Tree (descriptive set theory)

In descriptive set theory, a "tree" is a mathematical structure that represents a collection of finite sequences, often used in the study of Polish spaces (complete separable metric spaces) and Borel sets. Trees can be used to analyze various concepts in set theory, including definability and complexity of sets and functions. A tree is typically defined as a set \( T \) of finite sequences of elements drawn from a given set \( X \).