RadTreeView Node not getting checked from code behind.

function ToggleChecks(RadTreeView) {

    var RadTreeView1 = $find(RadTreeView);

    if (RadTreeView1._nodeData[0] != undefined) {
        var node = '';
        for (var i = 0; i < RadTreeView1._nodeData[0].items.length; i++) {
            if (RadTreeView1._nodeData[0].items[i].text != null) {
                node = RadTreeView1._findItemByText(RadTreeView1._nodeData[0].items[i].text);
            }
            else {
                node = RadTreeView1._findItemByValue(RadTreeView1._nodeData[0].items[i].value);
            }
            if (RadTreeView1._nodeData[0].items[i].checked == true) {
                node.uncheck();
            }
            else {
                RadTreeView1._nodeData[0].items[i].checked = 1;
                node.check();
            }
        }


    }
    return false;
}