Force-Directed Tree

This randomly-generated tree is positioned using a force simulation.

<!DOCTYPE html>
<meta charset="utf-8">
<canvas width="960" height="960"></canvas>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script>
function getData (data) {
  let nested = d3.nest().key(d => d["Session #"]).entries(data)
  let root = {};
  let parent;
  
  let maxLevel = d3.max(nested, d => d.values.length) - 1;
  
  for (let i = 0; i < maxLevel; i++) {
    let levelActions = getLevelActions(i);
    if (i === 0) {
      root.actionText = levelActions[0].actionText;
      root.children = [];
    } else {
      levelActions.forEach(d => {
        if (parent) {
          let _parent = parent.filter(x => x.actionText === d.parent 
                                      && x.sessions.indexOf(d.sessions[0]) > -1);
          if (_parent.length) {
            if (!_parent[0].children)
              _parent[0].children = [];
            _parent[0].children.push(d)
          }
        } else {
          root.children.push(d)
        }
      })
      parent = levelActions;
    }
  }
  
  function getLevelActions(level) {
    let actions = [];
    for (let j = 0; j < nested.length; j++) {
      let values = nested[j].values;
      if (!values[level]) continue;

let x0 = Infinity;
  let x1 = -x0;
  let maxDepth = 0;
  root.each(d => {
    if (d.x > x1) x1 = d.x;
    if (d.x < x0) x0 = d.x;
    if (d.depth > maxDepth) maxDepth = d.depth
  });

var nodes = root.descendants().reverse();
  var links = root.links();
	var simulation = d3.forceSimulation(nodes)
    .force("charge", d3.forceManyBody())
    .force("link", d3.forceLink(links).distance(20).strength(1))
    .force("x", d3.forceX())
    .force("y", d3.forceY())
    .on("tick", ticked);

var canvas = document.querySelector("canvas"),
    context = canvas.getContext("2d"),
    width = canvas.width,
    height = canvas.height;

d3.select(canvas)
		.attr('height', height)
    .call(d3.drag()
        .container(canvas)
        .subject(dragsubject)
        .on("start", dragstarted)
        .on("drag", dragged)
        .on("end", dragended));

function ticked() {
  context.clearRect(0, 0, width, height);
  context.save();
  context.translate(width / 2, height / 2);

context.beginPath();
  links.forEach(drawLink);
  context.strokeStyle = "#aaa";
  context.stroke();

context.beginPath();
  nodes.forEach(drawNode);
  context.fill();
  context.strokeStyle = "#fff";
  context.stroke();

context.restore();
}

function dragsubject() {
  return simulation.find(d3.event.x - width / 2, d3.event.y - height / 2);
}

function dragstarted() {
  if (!d3.event.active) simulation.alphaTarget(0.3).restart();
  d3.event.subject.fx = d3.event.subject.x;
  d3.event.subject.fy = d3.event.subject.y;
}

function dragged() {
  d3.event.subject.fx = d3.event.x;
  d3.event.subject.fy = d3.event.y;
}

function dragended() {
  if (!d3.event.active) simulation.alphaTarget(0);
  d3.event.subject.fx = null;
  d3.event.subject.fy = null;
}

function drawLink(d) {
  context.moveTo(d.source.x, d.source.y);
  context.lineTo(d.target.x, d.target.y);
}

function drawNode(d) {
  context.moveTo(d.x + 3, d.y);
  context.arc(d.x, d.y, 3, 0, 2 * Math.PI);
}

})

</script>

https://d3js.org/d3.v4.min.js