Hi Alberto,

You can add XamWebTree like a content of the some of OutlookBarGroup:

You can have XamWebOutlookBar with groups:

        <igOB:XamWebOutlookBar x:Name="xamOB" Grid.Column="1" Width="150" MinimizedWidth="70" ShowToolTips="True" IsMinimized="True"
               ToolTipService.ToolTip="OBTooltip" HorizontalAlignment="Left">
            <igOB:OutlookBarGroup x:Name="Gr1" Key="Group1" >
                <Button Content="Button1" ToolTipService.ToolTip="AAA"/>
            </igOB:OutlookBarGroup>
            <igOB:OutlookBarGroup x:Name="Gr2" Key="Group2" ToolTip="Group2ToolTip">
                <Controls:XamWebTree x:Name="xamWebTree" Width="200" Height="350" Grid.Column="0">
                    <Controls:XamWebTreeItem x:Name="ItemX" Header="Item X" MouseLeftButtonDown="Item_MouseLeftButtonDown"/>
                </Controls:XamWebTree>
            </igOB:OutlookBarGroup>
            <igOB:OutlookBarGroup x:Name="Gr3" Key="Group3" >
                <Grid></Grid>
            </igOB:OutlookBarGroup>
        </igOB:XamWebOutlookBar>

It is possible to add XamWebTree as a content of OutlookBarGroup in XAML or

create and add it like a content of any OutlookBarGroup:

         XamWebTree sampleTree = new XamWebTree();

            XamWebTreeItem itemA = new XamWebTreeItem
            {
                Name = "itemA",
                Header = "Item A"
            };
            sampleTree.Items.Add(itemA);
            XamWebTreeItem itemB = new XamWebTreeItem
            {
                Name = "itemB",
                Header = "Item B"
            };
            sampleTree.Items.Add(itemB);
            XamWebTreeItem itemC = new XamWebTreeItem
            {
                Name = "itemC",
                Header = "Item C"
            };
            sampleTree.Items.Add(itemC);

            this.xamOB.Groups["Group3"].Content = sampleTree;

I hope this can help :-)

Best Wishes!

Mihail