Recursive function for parsing a tree and building some HTML

TreeParser.js

      var tree = {
            a : {value : "This is node A", parent : ""},
            b : {value : "This is node B", parent : "a"},
            c : {value : "This is node C", parent : "a"},
            d : {value : "This is node D", parent : "c"},
            e : {value : "This is node E", parent : "c"},
            f : {value : "This is node F", parent : "c"}
      }
    
      var buildTree = function (obj, node) {
        var treeString = "<ul><li>" + obj[node].value;
          for (var i in obj) {
            if (obj[i].parent == node) {
              treeString += buildTree(obj, i);					
            }
          }
        treeString += "</li></ul>";
        return treeString;
      }
      
      document.getElementById("tree").innerHTML = buildTree(tree, "a");