Having problems dynamicaly loading the tree structure

Refering to the tree example provided

am filling the array tree in this fashion

var tree = new Array();
var treeArr = new Array();
treeArr[0] = "1,2,3,4,5,6";
tree[0] = tree[0].split(",");
tree[1] = [7,8,9];

this works perfectly ok given the appropriate text values.
This problem arises when I try to load the tree array dynamicaly like this

var treeArr = "1,2,3,4,5,6+7,8,9".split("+");
var tree = new Array();
for(var i=0;i<treeArr .length;i++){
if(treeArr [i].length > 0){
tree[i] = treeArr [i].split(",");
}
}

now this piece of code although symantically same as above doesnt
render the tree as piece code above does.