title: Sorting TreeMap alphabetically
body: <p>I have an object of typer person, which has a name as attribute.
  I have a treemap which link the person to a distance, which is an integer.</p>
  
  <p>I need to sort the TreeMap in alphabetical order, by looking at the name of each person in it.</p>
  
  <p>How can I do that ? 
  thank you for your answers.</p>