void ParserTreeItem::add(const ParserTreeItem::ConstPtr &target)
{
    if (target.isNull())
        return;

    // add locations
    d->symbolLocations = d->symbolLocations.unite(target->d->symbolLocations);

    // add children
    // every target child
    CitSymbolInformations cur = target->d->symbolInformations.constBegin();
    CitSymbolInformations end = target->d->symbolInformations.constEnd();
    while (cur != end) {
        const SymbolInformation &inf = cur.key();
        const ParserTreeItem::Ptr &targetChild = cur.value();

        ParserTreeItem::Ptr child = d->symbolInformations.value(inf);
        if (!child.isNull()) {
            child->add(targetChild);
        } else {
            ParserTreeItem::Ptr add(new ParserTreeItem());
            add->copyTree(targetChild);
            d->symbolInformations[inf] = add;
        }
        // next item
        ++cur;
    }
}