Hi there, In this case, you can customise the TreeView control to do what you want. You can create a custom TreeNode as below and override the RenderPreText/RenderPostText method:
public class ExTreeNode : TreeNode
{
protected override void RenderPreText(HtmlTextWriter writer)
{
base.RenderPreText(writer);
writer.AddAttribute("onmouseover", "alert('hover me')");
}
}
Also, to make the TreeView control work properly on postback, you may need to create a custom TreeView control by inheriting the built-in control and override the protected CreateNode method.