Tree Distances

A tree is defined as a connected, undirected graph with $n$ vertices and $n−1$ edges. The distance between two vertices in a tree is equal to the number of edges on the unique simple path between them. You are given two integers $x$ and $y$. Construct a tree with the following properties: - The number of pairs of vertices with an **even** distance between them equals $x$. - The number of pair