XUL Tree: a javascript widget

Here is a piece of code I wrote to be able to assemble XUL Tree from a given javascript object.

/*****************************************************
EXAMPLE OF CONFIG OBJECT
/*****************************************************
var oConfig = {
 id: "mytree",
 className: "classname"
 treecols: [{
   label: "Column 1",
   primary: true,
   id: "col1"
  },{
   label: "Column 2",
   id: "col2",
  }
 ]
}
/*****************************************************
EXAMPLE OF DATA OBJECT
/*****************************************************
var oData = {
 open: true,
 cols: [
  { label: 'node1' },
  { label: 'node2' }
 ],    
 nodes: [
  {
   cols: [
    { label: 'node3' },
    { label: 'node4' }
   ],    
   nodes: []
  },{
   cols: [
    { label: 'node5' },
    { label: 'node6' }
   ],    
   nodes: []
  }
 ]
};
/*****************************************************/
function tree(sContainer, oConfig, oData) {
 this.container = document.getElementById(sContainer);
 this.data = oData;
 this.config = oConfig;
 // create tree
 this.tree = document.createElement('tree');
 this.tree.setAttribute('flex','1');
 // create treecols
 this.treecols = document.createElement('treecols');
 this.cols = [];
 var nOrdinal = 1;
 for(var i in this.config.cols) {
  var oCol = document.createElement('treecol');
  oCol.setAttribute('label',this.config.cols[i].label);
  oCol.setAttribute('primary',this.config.cols[i].primary);
  oCol.setAttribute('id',this.config.cols[i].id);
  oCol.setAttribute('ordinal',nOrdinal++);
  oCol.setAttribute('flex','1');
  this.cols.push(oCol);
  var oSplitter = document.createElement('splitter');
  oSplitter.setAttribute('ordinal',nOrdinal++);
  this.treecols.appendChild(oCol);
  if(i < this.config.cols.length - 1) {
   this.treecols.appendChild(oSplitter);
  }
 }
 this.tree.appendChild(this.treecols);
 this.container.appendChild(this.tree);
 
 this.root = document.createElement('treechildren');
 this.createNode(this.root, this.data);
 this.tree.appendChild(this.root);
}
/*****************************************************/
tree.prototype.createNode = function(oParent, oNodeData) {
 var oTreeItem = document.createElement('treeitem');
 if(oNodeData.open) {
  oTreeItem.setAttribute('open',oNodeData.open);
 }
 var oTreeRow = document.createElement('treerow');
 for(var i=0; i<oNodeData.cols.length; i++) {
  var oTreeCell = document.createElement('treecell');
  oTreeCell.setAttribute('label',oNodeData.cols[i].label);
  oTreeRow.appendChild(oTreeCell);
 }
 oTreeItem.appendChild(oTreeRow);
 if(oNodeData.nodes) {
  oTreeItem.setAttribute('container','true');
  var oTreeChildren = document.createElement('treechildren');
  for(var i=0; i<oNodeData.nodes.length; i++) {
   this.createNode(oTreeChildren,oNodeData.nodes[i]);
  }
  oTreeItem.appendChild(oTreeChildren);
 }
 oParent.appendChild(oTreeItem);
}
/*****************************************************