fn append_children(node : &mut Node, nodes : &HashMap<&str, Vec<&str>>) {
    if let Some(n_arr) = nodes.get(node.name) {
        for n in n_arr {
            node.children.push(Node { name : n, children : Vec::new() });
            append_children(&mut node.children[node.children.len()-1], nodes);
        }
    }
}