I have a big node tree that I would like to collapse into a single node with custom inputs (in shading you can do that pressing ctrl-g), is that possible? Thanks!
You can, but it works differently than in the Shader Node tree. You don't have a "Sublayer" tree where you go and edit the node group's insides.
You first add a Group Input node by going Add > Subprograms > Group
Then you can add operations like in regular subprograms. Make sure you don't have circular dependencies and that all the group logic is contained within it. The nodes will take the color of the group by default.
To get ouput values, click on Output Node on the bottom of the Group Input node and link it as you wish.
You can Invoke the Group by going Add > Subprograms > - My Group (You can change the name in the Input node).