moving down
function tree() {
  pu(); bk(350); pd();
  fd(150); vee(100);
}
function test() {
  tree();
}

Now to work on making the branches smaller as the tree "grows".

I plan to start with a width of 4 and reduce this by a factor of .8 each vee. You should be able to do this before  clicking here to reveal my answer.

function vee(d,w) {
  if (d>10) {
    var f=.8;
    pw(w);
    lt(30);
    fd(d); vee(d*f,w*f);
    pw(w);
    bk(d); rt(60);
    fd(d); vee(d*f,w*f);
    pw(w);
    bk(d); lt(30);
  }
}
function tree() {
  pu(); bk(350); pd();
  pw(4); fd(150); vee(100,4);
}

Notice how after each call to vee, I reset the width.