Hey,

I'm not sure whether you mean to expand a root row or a row in level one, but that shouldn't matter too much, unless you are also using LoadOnDemand, which would make it hard on the client.  To expand a row on the client, try the following.

function init(grid, args) {
            var grid = $find("WebHierarchicalDataGrid1");
            grid.get_gridView().get_rows().get_row(1).set_expanded(true);
        }

<ClientEvents Initialize="init" />

If you would rather do it on the server, I did it in the WebHierarchicalDataGrid's DataBound event.

protected void WebHierarchicalDataGrid1_DataBound(object sender, EventArgs e)
    {
        this.WebHierarchicalDataGrid1.GridView.Rows[1].Expanded = true;
    }

Let us know if you need more help.

regards,
David Young