MyObject* deleted_object = *((MyObject**)(((CTreeNode*)nd)->userData));
m_tree.DeleteNode((CTreeNode*)nd);
TREENODEHANDLE curCh = m_objects_node->pFirstChild;
while (curCh)
{
if ((*((sgCObject**)(curCh->userData)))==deleted_object) // <-----Вот тут
   m_tree.DeleteNode((CTreeNode*)curCh);
curCh = curCh->pNextSibling;
}