Excercise:
Attractor excercise
Learning to work with data tree with confidence will make you a pro GH user. This is what separates beginners from propper users.
06 - Data Tree
Here are some videos to help you understand more:
Cool playlist of short videos explaining data tree from the MODELAB guys:
https://www.youtube.com/playlist?list=PLGV167zE8gnVRrzCCWvdlHYh3XQWTXFDo
A single video going through the essentials of Data tree: