@NotNull
 private InspectionTreeNode getRelativeRootNode(
     boolean isGroupedBySeverity, HighlightDisplayLevel level) {
   if (isGroupedBySeverity) {
     InspectionSeverityGroupNode severityGroupNode = mySeverityGroupNodes.get(level);
     if (severityGroupNode == null) {
       InspectionSeverityGroupNode newNode = new InspectionSeverityGroupNode(myProject, level);
       severityGroupNode = ConcurrencyUtil.cacheOrGet(mySeverityGroupNodes, level, newNode);
       if (severityGroupNode == newNode) {
         InspectionTreeNode root = myTree.getRoot();
         addChildNodeInEDT(root, severityGroupNode);
       }
     }
     return severityGroupNode;
   }
   return myTree.getRoot();
 }