From Eclipsepedia

Add a dynamic submenu to the ProblemView menu

In Menu Contributions/Problems View Example we added 2 dynamic menus. You then have to implement CompoundContributionItem in your provided class.

     <menu id="org.eclipse.ui.views.problems.groupBy.menu"
           label="%ProblemView.GroupBy.label"
           mnemonic="%ProblemView.GroupBy.mnemonic">
       <dynamic class="org.eclipse.ui.views.markers.internal.GroupByItems"
                id="org.eclipse.ui.views.problems.groupBy.items"/>
     </menu>

When your menu is populated, you'll have your getContributionItems() method called:

protected IContributionItem[] getContributionItems() {
     IContributionItem[] list = new IContributionItem[2];
     Map parms = new HashMap();
     parms.put("groupBy", "Severity");
     list[0] = new CommandContributionItem(null,
             "org.eclipse.ui.views.problems.grouping",
             parms, null, null, null, "Severity", null,
             null, CommandContributionItem.STYLE_PUSH);

     parms = new HashMap();
     parms.put("groupBy", "None");
     list[1] = new CommandContributionItem(null,
             "org.eclipse.ui.views.problems.grouping",
             parms, null, null, null, "None", null, null,
             CommandContributionItem.STYLE_PUSH);
     return list;
}