private void addChildren(final ExplorerNode parent,
                             final List<ExplorerNode> children) {
        if (children == null) {
            return;
        }

        for (final ExplorerNode child : children) {
            parents.put(child, parent);
            addChildren(child, child.getChildren());
        }
    }
Get the set of selected items.

@return the set of selected items
stroom-core-client/src/main/java/stroom/explorer/client/presenter/TickBoxSelectionModel.java