You have to place your ribbon controls inside a DockPanel
:
<Ribbon.QuickAccessToolBar>
<RibbonQuickAccessToolBar>
<DockPanel>
<RibbonSplitButton x:Name ="Save" Label="Save" />
<RibbonSplitButton Label="Employee Access" LabelPosition="Header" >
<RibbonMenuItem Header="Undo action #1" />
<RibbonMenuItem Header="Undo action #2" />
<RibbonMenuItem Header="Undo action #3" />
</RibbonSplitButton>
</DockPanel>
</RibbonQuickAccessToolBar>
</Ribbon.QuickAccessToolBar>