$TREE Tree pairs are pairs of nodes in a tree whose relationship is considered for analysis—often ancestor–descendant, distance-based, or lowest common ancestor (LCA) related. In algorithms, counting specific tree pairs helps solve problems like shortest paths, communication delays, or subtree queries. For example, in a rooted tree, we might count pairs (u, v) where u is an ancestor of v, or pairs whose distance equals a given k. Efficient solutions use DFS, dynamic programming, or binary lifting to avoid O(n²) enumeration. Tree pair concepts are common in competitive programming, network modeling, and hierarchical data analysis for performance and optimization tasks.