code: protected void checkExpandedCustomNodes() {
  
  		TreeItemIdNode custom = getCustomTree();
  		if (custom == null) {
  			return;
  		}
  
  		// Get the expanded rows
  		Set<String> expanded = getExpandedRows();
  
  		// Process Top Level
  		for (TreeItemIdNode node : custom.getChildren()) {
  			processCheckExpandedCustomNodes(node, expanded);
  		}
  	}
docs: Check if custom nodes that are expanded need their child nodes added from the model.