# Using Additional Columns

If you need to map additional columns from the Data Source to properties of the RadTreeView Nodes, you can use the **NodeDataBound** event. The event arguments passed to the event, **e.Node**and **e.Node.DataItem**, hold the instance of the RadTreeView Node being bound and the **DataItem** to which it is bound. You can map a property from the **DataItem** to the corresponding property of the RadTreeView Node. Be sure to cast the **DataItem** object to the proper data type first.

In the example below, the **RadTreeView** is bound to a **DataTable** and the **DataItem** is of type **DataRowView**. If you were binding to an array of a custom object "Employee", then the **DataItem** would be cast to the **Employee** type before using.

```C#
protected void RadTreeView1_NodeDataBound(object sender, RadTreeNodeEventArgs e) 
{ 
    e.Node.ToolTip = (e.Node.DataItem as DataRowView)["Description"].ToString(); 
}
```

```VB.NET
Protected Sub RadTreeView1_NodeDataBound(ByVal sender As Object, ByVal e As RadTreeNodeEventArgs)
    e.Node.ToolTip = (TryCast(e.Node.DataItem, DataRowView))("Description").ToString()
End Sub	
```