我如何开始d3.js树在一个折叠的位置

我得到了d3.js代码来创建树，我很高兴地做了，但我不知道如何开始树倒塌。

我发现这篇文章解释了如何做到这一点，但它似乎没有对我的代码做任何事情:Edit the javascript to switch the _children and children attributes for every node. This could be done like so

var treeData = [
{
    "name": "Product",
        "parent": "null",
        "children": [
    <!-------------- BRANCH ----------->	
    {
        "name": "Servers",
            "parent": "Top Level",
            "children": [{
            "name": "Options (Hard disk / RAM / PSU / Network cards etc)",
                "parent": "Servers"
        }, {
            "name": "Software licensing – Microsoft O/S?",
                "parent": "Servers"
        }, {
            "name": "Switching – HP / Cisco",
                "parent": "Servers"
        }, {
            "name": "UPS – APC",
                "parent": "Servers"
        }, {
            "name": "Cabling",
                "parent": "Servers"
        }, {
            "name": "Warranty – Ecare+ / HP Care Pack?",
                "parent": "Servers"
        }, {
            "name": "Engineer Installation – on-site / remote log-in?",
                "parent": "Servers"
        }, {
            "name": "Config centre – Build & test server and parts prior to delivery",
                "parent": "Servers"
        }, {
            "name": "Telephone support credits",
                "parent": "Servers"
        }
        ]
    },
    <!-------------- BRANCH ----------->		  
    {
        "name": "PC/Laptop/Workstation",
            "parent": "Top Level",
            "children": [{
            "name": "Monitor",
                "parent": "PC/Laptop/Workstation"
        }, {
            "name": "Docking Station",
                "parent": "PC/Laptop/Workstation"
        }, {
            "name": "Microsoft Office license",
                "parent": "PC/Laptop/Workstation"
        }, {
            "name": "Carry Case (laptop)",
                "parent": "PC/Laptop/Workstation"
        }, {
            "name": "Accessories – Mouse/Keyboard/Riser/Keylock",
                "parent": "PC/Laptop/Workstation"
        }, {
            "name": "Config centre – desktop imaging/adding 2nd HD or RAM",
                "parent": "PC/Laptop/Workstation"
        }, {
            "name": "On-site installation – desktop rollout",
                "parent": "PC/Laptop/Workstation"
        }, {
            "name": "Telephone Support credits",
                "parent": "PC/Laptop/Workstation"
        }
        ]
    },
    <!-------------- BRANCH ----------->		  
    {
        "name": "Switches",
            "parent": "Top Level",
            "children": [{
            "name": "SFP/Transceivers",
                "parent": "Switches"
        }, {
            "name": "Cables",
                "parent": "Switches"
        }, {
            "name": "Config Centre – pre-delivery config work",
                "parent": "Switches"
        }, {
            "name": "Network cards",
                "parent": "Switches"
        }, {
            "name": "On-site installation",
                "parent": "Switches"
        }
        ]
    },

    <!-------------- BRANCH ----------->	  
    <!-------------- END ----------->	
    ]
},
];
// ************** 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 + "," + 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 * 250;
    });
    // 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", "node")
        .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", "link")
        .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);
}

	.node {
	    cursor: pointer;
	}
	.node circle {
	    fill: #fff;
	    stroke: steelblue;
	    stroke-width: 3px;
	}
	.node text {
	    font: 12px sans-serif;
	    background-color:##
	}
	.link {
	    fill: none;
	    stroke: #ccc;
	    stroke-width: 2px;
	}
	

<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.0.4/d3.min.js"></script>