struct TreeList
{
    static bool BeginTree(const char* const names)
    {
        // [TODO] put that ID in a deeper storage...
        ImGuiID identation_id = ImGui::GetID("identation_int");
        ImGuiStorage* storage = ImGui::GetStateStorage();
        storage->SetInt(identation_id, 0);

        return ImGui::CollapsingHeader(names);
    }

    // Returns true if the node is expanded.
    static bool Node(
        const char* const label, // The label of the node(mind 2 nodes with equal names).
        const std::function<void()>& usrCode, // user desiered GUI, state storage is implemented by the user.
        bool showExpandBtn) // aka. has any children.
    {
        ImGuiStorage* storage = ImGui::GetStateStorage();

        ImGuiID expanded_vect_id = ImGui::GetID("expanded_vect");
        ImGuiID selection_vect_id = ImGui::GetID("selection_vect");
        ImGuiID identation_id = ImGui::GetID("identation_int");

        std::vector<std::string>* pExpanded = (std::vector<std::string>*)storage->GetVoidPtr(expanded_vect_id);

        int lebelIdx = storage->GetInt(identation_id, 0);

        if(pExpanded == NULL)
        {
            pExpanded = new std::vector<std::string>();
            storage->SetVoidPtr(expanded_vect_id, pExpanded);
        }

        std::vector<std::string>& expanded = *pExpanded;
        const auto itrExpanded = std::find(std::begin(expanded), std::end(expanded), label);
        const bool wasExpanded = itrExpanded != expanded.end();

        ImGui::PushID(label);

        lebelIdx++;
        storage->SetInt(identation_id, lebelIdx);

        bool newExpanded = false;
        if(showExpandBtn)
        {
            newExpanded = ImGui::SmallButton(wasExpanded ? "-" : "+") ? !wasExpanded : wasExpanded;
        }
        else
        {
            ImGui::Text(""); // Something to be on the same line.
        }

        usrCode();

        ImGui::PopID();

        if(newExpanded == false)
        {
            if(wasExpanded)
            {
                expanded.erase(itrExpanded);
            }
        }
        else if(wasExpanded == false)
        {

            expanded.push_back(label);
        }

        if(newExpanded)
        {
            ImGui::Indent();
        }

        return newExpanded;
    }

    static void NodeEnd()
    {
        ImGui::Unindent();
    }
};