code: public Tree putSet(String path, boolean putIfAbsent) {
  		return putObjectInternal(path, new LinkedHashSet<Object>(), putIfAbsent);
  	}
docs: Associates the specified Set container with the specified path. If the
  structure previously contained a mapping for the path, the old value is
  replaced. Set similar to List, but contains no duplicate elements. Sample
  code:<br>
  <br>
  Tree node = new Tree();<br>
  <br>
  Tree set1 = node.putSet("a.b.c");<br>
  set1.add(1).add(2).add(3);<br>
  <br>
  Tree set2 = node.putSet("a.b.c", true);<br>
  set2.add(4).add(5).add(6);<br>
  <br>
  The "set2" contains 1, 2, 3, 4, 5 and 6.
  
  @param path
  path with which the specified Set is to be associated
  @param putIfAbsent
  if true and the specified key is not already associated with a
  value associates it with the given value and returns the new
  Set, else returns the previous Set
  
  @return Tree of the new Set