// 桉树的可视顺序遍历
for ( tree_type::iterator it = thetree.begin(); thetree.end() != it; ++ it )
{
// do something here, visit the element reference by *it
}

// 桉树的可视顺序倒着遍历
for ( tree_type::reverse_iterator it = thetree.rbegin(); thetree.rend() != it; ++ it )
{
// do something here, visit the element reference by *it
}

// 也可以通过parent、next_sibling、prev_sibling、first_child、last_child等自定义遍历顺序