Reading root files examples

[DanielWielanek]

Many experiments would like to compress data produced by FairRoot framework. They are do this by using some custom trees. In similar way they also store "pure MC" data from generators. However I cannot read an example that show how can I read such files.

It will be nice to have some examples how to read and store data in custom tree. Actually I know that reading is possible by FairSource-based class but I have no idea how to write custom tree.