var expandedNodes = new BindingList<String>();
foreach (var node in ultraTree1.Nodes)
{
	if (node.Expanded)
	{
		expandedNodes.Add(node.Key);
	}
}

ultraTree1.BeginUpdate();
this.parentTableAdapter.Fill(this.dataSet1.Parent);
this.childTableAdapter1.Fill(this.dataSet1.Child);
ultraTree1.EndUpdate();

foreach (var key in expandedNodes)
{
		var node = ultraTree1.Nodes[key];
		node.Expanded = true;
}

Code had a defunct dependency, but this is the gist of it.