让树状控件显示展开和折叠的按钮其实是很简单的，把 Style 设置成TVS_HASBUTTONS就可以了。不过你可能会发现根节点却没有展开折叠按钮，咋回事呢？折腾半天也没作用，还是看看MSDN的文档吧。
TVS_HASBUTTONS
Displays plus (+) and minus (-) buttons next to parent items. The user clicks the buttons to expand or collapse a parent item’s list of child items. To include buttons with items at the root of the tree view, TVS_LINESATROOT must also be specified.
呵呵，注意到了吧，最后一句，还需要 TVS_LINESATROOT。这就够了吗？再看看 TVS_LINESATROOT
TVS_LINESATROOT
Uses lines to link items at the root of the tree-view control. This value is ignored if TVS_HASLINES is not also specified.
如果 TVS_HASLINES 没有设置，那么 TVS_LINESATROOT将会被忽略，所以也别忘了 TVS_HASLINES。再看TVS_HASLINES。
TVS_HASLINES
Uses lines to show the hierarchy of items.
看来不需要其他的了，试一试，可以了吧。呵呵。
