connect(this, SIGNAL(collapsed(const QModelIndex &)), this, SLOT(on_collapse(const QModelIndex &)));
connect(this, SIGNAL(expanded(const QModelIndex &)), this, SLOT(on_expand(const QModelIndex &)));
connect(this, SIGNAL(collapsed(const QModelIndex &)), this, SLOT(on_collapse(const QModelIndex &)));
connect(this, SIGNAL(expanded(const QModelIndex &)), this, SLOT(on_expand(const QModelIndex &)));