The Tree class is completely agnostic of any notion of a dependency
tree. So it's filter and reverse methods purely work on the given
datastructure which is a map. So the combination of '--reverse' and
'--packages' options require the reverse method to be called before
filter. If done the other way, when reverse is called, it will have
only partial tree resulting in incorrect behaviour in the context of
this script.
Added documentation on the tree class and it's methods accordingly.
Vineet Naik