class Sorter
{
public:
    static int compareElements(const juce::ValueTree& a, const juce::ValueTree& b)
    {
        int apos = static_cast<int>(a.getProperty("position"));
        int bpos = static_cast<int>(b.getProperty("position"));
        return (apos < bpos) ? -1 : ((bpos < apos) ? 1 : 0);
    }
};


struct Parent : public ValueTree::Listener
{
    Parent(UndoManager* u)
    : tree(ValueTree("parent")),
      undo(u)
    {
        tree.addListener(this);
    }

  void valueTreePropertyChanged(juce::ValueTree& s, const juce::Identifier& p) override {}
  void valueTreeChildRemoved(juce::ValueTree& t, juce::ValueTree& t1, int i) override {}
  void valueTreeChildOrderChanged(juce::ValueTree& t, int i, int i1) override {}
  void valueTreeParentChanged(juce::ValueTree& t) override {}
  void valueTreeChildAdded(juce::ValueTree& p, juce::ValueTree& c) override
  {
    Sorter s;
    tree.sort(s, undo, false);
  }

  void add(ValueTree c)
  {
    tree.addChild(c, -1, undo);
  }

  ValueTree tree;
  UndoManager* undo;
};


int main(int argc, char** argv)
{
    UndoManager undoManager;

    Parent parent(&undoManager);

    parent.add(ValueTree{"child1", {{ "position", 0}}});
    parent.add(ValueTree{"child2", {{ "position", 1000}}});

    undoManager.beginNewTransaction();

    parent.add(ValueTree{"child3", {{ "position", 500}}});

    std::cout << parent.tree.toXmlString() << "\n";

    undoManager.undo();

    std::cout << parent.tree.toXmlString() << "\n";
}