递归
id     name    parent
1      财务      2
2      总部      0
3      人事一   4
4      人事      2
5      财务二   1
6      行政      2
7      人事二   4
8      财务一   1
9      人事三   4 
层级递归

------解决方案--------------------
http://www.cnblogs.com/xiao793/archive/2010/04/20/1716407.html