var a = document.getElementById("myCanvas");
var b = a.getContext("2d");

var angle = 0.5;
var branchScale = 0.75;
var l = 60;
var minL = 5;
var w = b.canvas.width;
var h = b.canvas.height;

b.translate(w/2, h);
drawBranch(l, 0);

function drawBranch(l, direction) {
  b.save();
  var a = angle * Math.random();
  b.rotate(a * direction);
  b.fillStyle = "#1e8214";
  b.fillRect(-l / 20, 0, l / 10, -l);
  if (l > minL) {
    b.translate(0, -l);
    var c = 0.2 * (Math.random() - 0.5);
    c = c + 1;
	b.fillStyle = "#1e8214";
    drawBranch(l * c * branchScale, -1);
    c = 1 + 0.2 * (Math.random() - 0.5);
    drawBranch(l * c * branchScale, 1);
  }
  b.restore();
}