code: function(obj, callback){
  	        if (obj){
  
  	            if (obj.left !== null){
  	                inOrder(obj.leftchild, callback);
  	            }            
  
  	            callback.call(this,obj.element);
  
  	            if (obj.right !== null){
  	                inOrder(obj.rightchild, callback);
  	            }
  	        }
  	    }
docs: **********************************
  Private functions
  **********************************