Tree layout with root collapsed

<!DOCTYPE html>
<html>
  <head>
    <meta http-equiv="Content-Type" content="text/html;charset=utf-8">
    <script type="text/javascript" src="https://cdn.jsdelivr.net/npm/d3@1.29.5/d3.js"></script>
    <script type="text/javascript" src="https://cdn.jsdelivr.net/npm/d3@1.29.5/d3.layout.js"></script>
    <style type="text/css">

.node rect {
  cursor: pointer;
  fill: #fff;
  fill-opacity: .5;
  stroke: #3182bd;
  stroke-width: 1.5px;
}

.node text {
  font: 10px sans-serif;
  pointer-events: none;
}

path.link {
  fill: none;
  stroke: #9ecae1;
  stroke-width: 1.5px;
}

</style>
</head>
<body>
    <div id="chart"></div>

var w = 960,
    h = 800,
    i = 0,
    barHeight = 20,
    barWidth = w * .8,
    duration = 400,
    root;

var tree = d3.layout.tree()
    .size([h, 100]);

var diagonal = d3.svg.diagonal()
    .projection(function(d) { return [d.y, d.x]; });

var vis = d3.select("#chart").append("svg:svg")
    .attr("width", w)
    .attr("height", h)
  .append("svg:g")
    .attr("transform", "translate(20,30)");

d3.json("flare.json", function(json) {
  json.x0 = 0;
  json.y0 = 0;
  update(root = json);
  click(root);
});

function update(source) {

// Compute the flattened node list. TODO use d3.layout.hierarchy.
  var nodes = tree.nodes(root);
  
  // Compute the "layout".
  nodes.forEach(function(n, i) {
    n.x = i * barHeight;
  });
  
  // Update the nodes…
  var node = vis.selectAll("g.node")
      .data(nodes, function(d) { return d.id || (d.id = ++i); });
  
  var nodeEnter = node.enter().append("svg:g")
      .attr("class", "node")
      .attr("transform", function(d) { return "translate(" + source.y0 + "," + source.x0 + ")"; })
      .style("opacity", 1e-6);

// Enter any new nodes at the parent's previous position.
  nodeEnter.append("svg:rect")
      .attr("y", -barHeight / 2)
      .attr("height", barHeight)
      .attr("width", barWidth)
      .style("fill", color)
      .on("click", click);
  
  nodeEnter.append("svg:text")
      .attr("dy", 3.5)
      .attr("dx", 5.5)
      .text(function(d) { return d.name; });
  
  // Transition nodes to their new position.
  nodeEnter.transition()
      .duration(duration)
      .attr("transform", function(d) { return "translate(" + d.y + "," + d.x + ")"; })
      .style("opacity", 1);
  
  node.transition()
      .duration(duration)
      .attr("transform", function(d) { return "translate(" + d.y + "," + d.x + ")"; })
      .style("opacity", 1)
    .select("rect")
      .style("fill", color);
  
  // Transition exiting nodes to the parent's new position.
  node.exit().transition()
      .duration(duration)
      .attr("transform", function(d) { return "translate(" + source.y + "," + source.x + ")"; })
      .style("opacity", 1e-6)
      .remove();
  
  // Update the links…
  var link = vis.selectAll("path.link")
      .data(tree.links(nodes), function(d) { return d.target.id; });
  
  // Enter any new links at the parent's previous position.
  link.enter().insert("svg:path", "g")
      .attr("class", "link")
      .attr("d", function(d) {
        var o = {x: source.x0, y: source.y0};
        return diagonal({source: o, target: o});
      })
    .transition()
      .duration(duration)
      .attr("d", diagonal);
  
  // Transition links to their new position.
  link.transition()
      .duration(duration)
      .attr("d", diagonal);
  
  // Transition exiting nodes to the parent's new position.
  link.exit().transition()
      .duration(duration)
      .attr("d", function(d) {
        var o = {x: source.x, y: source.y};
        return diagonal({source: o, target: o});
      })
      .remove();
  
  // Stash the old positions for transition.
  nodes.forEach(function(d) {
    d.x0 = d.x;
    d.y0 = d.y;
  });
}

// Toggle children on click.
function click(d) {
  if (d.children) {
    d._children = d.children;
    d.children = null;
  } else {
    d.children = d._children;
    d._children = null;
  }
  update(d);
}

function color(d) {
  return d._children ? "#3182bd" : d.children ? "#c6dbef" : "#fd8d3c";
}

</script>
  </body>
</html>

Modified http://mbostock.github.com/d3/d3.js?1.27.2 to a secure url

Modified http://mbostock.github.com/d3/d3.layout.js?1.27.2 to a secure url

https://mbostock.github.com/d3/d3.js?1.27.2

https://mbostock.github.com/d3/d3.layout.js?1.27.2