Adding Groups to SVG

<!DOCTYPE html>
<head>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v4.min.js"></script>
  <style>
    body { margin:0;position:fixed;top:0;right:0;bottom:0;left:0; }
  </style>
</head>

<body>
  <script>
  d3.json("data.json", function(error, json)  {
    console.log(json)
    var svg = d3.select("body").append("svg")	
  	.attr("width", 960)
  	.attr("height", 500)
  	var group = d3.select("svg").selectAll("g")
    	.data(json)
   		.enter()
  		.append("svg:g");
    	group.append("rect") 
  			.attr("y", function (d) {
        	if (d.orientation == "forward") {return 125;}
        	else if (d.orientation == "reverse") {return 200}})
      	.attr("height", 50)
    		.attr("x", function(d) {return  d.start}) 
  	  	.attr("width", function(d) {return d.stop - d.start}) 
    		.attr("fill", function(d) {if (d.orientation == "forward") {return "green" ;}
  						else if(d.orientation == "reverse"){return "red";}})
      	.style("stroke", "black")
    		.style("stroke-width", 3)
   		group.append("text")
      	.text(function (d) {return d.name})
        .attr ("height" , 50)  
        .attr("width" , 50)
        .attr("y", function (d) {
        	if (d.orientation == "forward") {return 150;}
        	else if (d.orientation == "reverse") {return 225;}})
      	.attr ("x", function(d) {return d.start + 15})
      	.style("font-size", 22)
      	.style("font-family", "monospace")
      	.style("fill", "black")})
    
  </script>
</body>

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