The snippet code below shows how to obtain checked nodes of WebTreeView in code behind (C#).

protected void Button1_Click(object sender, EventArgs e){
    TextBox1.Text = "Checked nodes are : \n";

    for (int i = 0; i < WebTreeView1.CheckedNodes.Count; i++)
    {
        WebTreeViewNode checkedNodes = WebTreeView1.CheckedNodes[i] as WebTreeViewNode;

        if (checkedNodes != null)
            TextBox1.Text += checkedNodes.Text + " ; \n";
    }
}

To obtain WebTreeView nodes, please try to use the Nodes property of WebTreeView. It is a collection of WebTreeViewNodeBinding. For example:

WebTreeViewNodeCollection nodes = WebTreeView1.Nodes;

Hope this help.