What does this Rust snippet output?

1enum Tree {
2    Leaf(i32),
3    Node(Box<Tree>, Box<Tree>),
4}
5fn sum(t: &Tree) -> i32 {
6    match t {
7        Tree::Leaf(v) => *v,
8        Tree::Node(l, r) => sum(l) + sum(r),
9    }
10}
11fn main() {
12    let t = Tree::Node(
13        Box::new(Tree::Leaf(1)),
14        Box::new(Tree::Leaf(2)),
15    );
16    println!("{}", sum(&t));
17}