public String traversePostorder(){
			String result="";
			Deque<Node> stack=new ArrayDeque<Node>();
			Node node;
			Node prevNode=null;
			stack.push(tree.getRootNode());
			while(!stack.isEmpty()){
				node=stack.peek();
				if(prevNode==null||prevNode.leftNode==node||prevNode.rightNode==node){
					if(node.leftNode!=null){
						stack.push(node.leftNode);
					}else if(node.rightNode!=null){
						stack.push(node.rightNode);
					}
				}else if(prevNode==node.leftNode){
					if(node.rightNode!=null){
						stack.push(node.rightNode);
					}
				}else if(prevNode==node){
					result+=node.data+" ";
					stack.pop();
				}
				prevNode=node;
			}
			
			return result;
		}