To reproduce:
public Form1()
{
    InitializeComponent(); 
    this.radTreeView1.NodesNeeded+=radTreeView1_NodesNeeded;
}

private void radTreeView1_NodesNeeded(object sender, Telerik.WinControls.UI.NodesNeededEventArgs e)
{
    Console.WriteLine("NodesNeeded"); 
}

As a result StackOverFlowException is thrown.

Workaround: Do not subscribe to the NodesNeeded event if the LazyMode property is set to false.