Treeview - sorting

Hi Everyone,
I had to write an app recently using treeview functionality and the user wanted to be able to re-sort the tree so I knocked up a script to do this (it's pretty basic but it seems to work!). 
Maybe it can help some of you who have asked about this topic in the Forum.
I can't say for certain if it works for every scenario and my app only uses one table but I imagine the general principle should still be valid. 
If it's of any use to anyone, please feel free to copy it, change it, improve on it etc.
I've left a bit of test data in it which means it's too large for here but it can be downloaded from this link
https://app.box.com/s/xozrjtjku8z21grc0x0n8433vidzbbxl
Regards,
Derek.