title: Perfect matching in a tree
body: <p>I came across a definition of Perfect matching: a set of edges that touches each node exactly once. </p>
  
  <p>However, i didnt really understand the definition. Can somebody give me an example of any such edge. Or may be point me towards some reference that does. </p>
  
  <p>I tried to google but it didnt give me any example. </p>