Definition
The chess tree (or game tree) is the branching structure of possible chess positions starting from a given position. Each node is a position; each branch is a legal move. The tree expands exponentially — about 35 legal moves per ply (half-move), so a 10-ply look-ahead branches into roughly 10²⁰ positions. A complete tree from the starting position has been estimated at 10⁴³ nodes.
Why it matters
How it works
Build the tree from the current position by enumerating legal moves at each node. Run minimax: at the maximizing player's nodes, take the maximum of children's values; at the minimizing player's nodes, take the minimum. Evaluate leaf positions with a static evaluator (material balance, mobility, king safety, pawn structure). Alpha-beta pruning skips branches that cannot affect the final decision, often pruning 99%+ of nodes. Practical depth is 10-30 plies depending on engine and time control.