Thank you! I didn't really get around to creating a bunch of examples. I have this wobbly tree though:

reset_changes();
let angle = 60;
rewire_calls("forward", {
    fn snake(n) {
        arc(n/2, angle);
        left(180);
        arc(n/2, -angle);
        left(180);
    }
    "snake"
});
rewire_calls("back", {
    fn snake_back(n) {
        left(180);
        snake(n);
        left(180);
    }
    "snake_back"
});

fn set_color(depth) {
    if depth < 3 {
        color(37, 102, 31);
    } else {
        color(73, 43, 16);
    }
}

fn tree(depth) {
    if depth == 0 {
        return;
    }

    let len = (depth+1).log() * 10;

    set_color(depth);
    left(angle/2);

    forward(len);
    tree(depth-1);
    back(len);

    right(angle);

    forward(len);
    tree(depth-1);
    back(len);

    left(angle/2);
    set_color(depth+2);
}

right(angle/2);
tree(6);
left(angle/2);
left(180);
reset_changes();
tree(6);
left(180);