Make tree structure from map object

tree.js

var tree = function(map)
{
    var treeStructure = {};
    var names;
    var name;
    var i;
    var numNames;
    var currentObject = treeStructure;
    var lastIndex;

    if (map)
    {
        for (var key in map)
        {
            var value = map[key];
            names = key.split(".");
            numNames = names.length;
            lastIndex = numNames-1;
            currentObject = treeStructure;

            for (i = 0; i < numNames; ++i)
            {
                name = names[i];

                if (i == lastIndex)
                {
                    currentObject[name] = value;
                }
                else if (!currentObject[name])
                {
                    currentObject[name] = {};
                }

                currentObject = currentObject[name];
            }
        }
    }

    return treeStructure;
};

usage

var myTree = tree(
{
   "user.name.first": "ola",
   "user.name.last": "normann",
   "user.age": 34,
   "user.bodyparts.arm.tattoes": ["snake", "anchor", "heart"]
});