#[derive(Debug)]
enum BinaryTree<T> {
    Empty,
    NonEmpty(Box<TreeNode<T>>)
}

#[derive(Debug)]
struct TreeNode<T> {
    element: T,
    left: BinaryTree<T>,
    right: BinaryTree<T>
}

impl<T: Ord> BinaryTree<T> {
    fn add(&mut self, value: T) {
        match *self {
            BinaryTree::Empty => *self = BinaryTree::NonEmpty(Box::new(TreeNode {
                element: value,
                left: BinaryTree::Empty,
                right: BinaryTree::Empty,
            })),
            BinaryTree::NonEmpty(ref mut node) => {
                if value <= node.element {
                    node.left.add(value);
                } else {
                    node.right.add(value);
                }
            }
        }
    }
}

fn main() {
    let mut tree = BinaryTree::Empty;
    tree.add("Mercury");
    tree.add("Venus");
    tree.add("Earth");
    tree.add("Mars");
    tree.add("Jupiter");
    tree.add("Saturn");
    tree.add("Uranus");
    tree.add("Neptune");
    tree.add("Pluto");

    println!("Tree: {:?}", tree);
}