code: function(tree, id) {
      if (tree.id == id)
        return tree;
      for ( var i = 0, ch = tree.children; i < ch.length; i++) {
        var t = this.getSubtree(ch[i], id);
        if (t != null)
          return t;
      }
      return null;
    }
docs: /*
  Method: getSubtree
  
  Returns the subtree that matches the given id.
  
  Parameters:
  
  tree - (object) A JSON tree object. See also <Loader.loadJSON>.
  id - (string) A node *unique* identifier.
  
  Returns:
  
  A subtree having a root node matching the given id. Returns null if no subtree matching the id is found.