StackOverflow: Fake multi-rooted tree

Faking a multi-rooted tree by using CSS to hide the root element. A more complete solution might have the animation of each branch starting at the first visible node, but this is a reasonable first pass.

For Stack Overflow question collapsible graph in d3: multiple root points

View the .block

<!DOCTYPE html>
<html lang="en">

<title>Tree Example</title>

.node circle {
      fill: #fff;
      stroke: steelblue;
      stroke-width: 3px;
    }

.node text {
      font: 12px sans-serif;
    }

.link {
      fill: none;
      stroke: #ccc;
      stroke-width: 2px;
    }

.level-0 {
      opacity: 0;
    }
  </style>

</head>

<body>

<script src="https://d3js.org/d3.v3.min.js"></script>

// ************** Generate the tree diagram	 *****************
    var margin = {
        top: 20,
        right: 120,
        bottom: 20,
        left: 120
      },
      width = 960 - margin.right - margin.left,
      height = 500 - margin.top - margin.bottom;

var i = 0,
      duration = 750,
      root;

var tree = d3.layout.tree()
      .size([height, width]);

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

var svg = d3.select("body").append("svg")
      .attr("width", width + margin.right + margin.left)
      .attr("height", height + margin.top + margin.bottom)
      .append("g")
      .attr("transform", "translate(" + (margin.left - 0) + "," + margin.top + ")");

root = treeData[0];
    root.x0 = height / 2;
    root.y0 = 0;

update(root);

d3.select(self.frameElement).style("height", "500px");

function update(source) {

// Compute the new tree layout.
      var nodes = tree.nodes(root).reverse(),
        links = tree.links(nodes);

// Normalize for fixed-depth.
      nodes.forEach(function(d) {
        d.y = d.depth * 120;
      });

// Update the nodes…
      var node = svg.selectAll("g.node")
        .data(nodes, function(d) {
          return d.id || (d.id = ++i);
        });

// Enter any new nodes at the parent's previous position.
      var nodeEnter = node.enter().append("g")
        .attr("class", function(d) {
          return 'node level-' + d.depth;
        })
        .attr("transform", function(d) {
          return "translate(" + source.y0 + "," + source.x0 + ")";
        })
        .on("click", click);

nodeEnter.append("circle")
        .attr("r", 1e-6)
        .style("fill", function(d) {
          return d._children ? "lightsteelblue" : "#fff";
        });

nodeEnter.append("text")
        .attr("x", function(d) {
          return d.children || d._children ? -13 : 13;
        })
        .attr("dy", ".35em")
        .attr("text-anchor", function(d) {
          return d.children || d._children ? "end" : "start";
        })
        .text(function(d) {
          return d.name;
        })
        .style("fill-opacity", 1e-6);

// Transition nodes to their new position.
      var nodeUpdate = node.transition()
        .duration(duration)
        .attr("transform", function(d) {
          return "translate(" + d.y + "," + d.x + ")";
        });

nodeUpdate.select("circle")
        .attr("r", 10)
        .style("fill", function(d) {
          return d._children ? "lightsteelblue" : "#fff";
        });

nodeUpdate.select("text")
        .style("fill-opacity", 1);

// Transition exiting nodes to the parent's new position.
      var nodeExit = node.exit().transition()
        .duration(duration)
        .attr("transform", function(d) {
          return "translate(" + source.y + "," + source.x + ")";
        })
        .remove();

nodeExit.select("circle")
        .attr("r", 1e-6);

nodeExit.select("text")
        .style("fill-opacity", 1e-6);

// Update the links…
      var link = svg.selectAll("path.link")
        .data(links, function(d) {
          return d.target.id;
        });

// Enter any new links at the parent's previous position.
      link.enter().insert("path", "g")
        .attr("class", function(d) {
          return 'link level-' + d.source.depth
        })
        .attr("d", function(d) {
          var o = {
            x: source.x0,
            y: source.y0
          };
          return diagonal({
            source: o,
            target: o
          });
        });

// 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);
    }
  </script>

</body>

</html>

Modified http://d3js.org/d3.v3.min.js to a secure url

https://d3js.org/d3.v3.min.js