Here’s my setup:
Currently all instanced splines are have the same diameter. But my goal is to have ability to set diameter by the first spline diameter/length. I.e. spline 1 should have diameter = 10, but spline 2 should have diameter = 0.1.
So basically each instanced lines should have lower and lower diameter based on how closer they to the tip of the first main spline.
Maybe someone have some examples for suck task?
i will help if you provide a blend file because i am too lazy to rebuild it…sorry
You need to do a few things :
The Spline parameter node / Factor will give you a value going from 0 to 1 along the curve,
You can use that to set the branches size.
That Attribute you need either to capture it , or store it at the beginning .
Then you need to use a realize instance so each branch can have a different radius,
And then use the attribute you stored earlier, maybe through a map range node to make different radius size
A simple tutorial either for a tree, or for a lightning should explain every details !
Good luck !
Thanks, Realize Instances helps 
I was a bit confused by have ability to change spawned splines length by change instance on points size, and by mistake think about it as a spline parameter 
Cool !
Yeah without the realize instance the change apply to the instance like if there is only one.
So changing the radius will have an effect . This behavior is powerful since if you have 100 000 instances the operation like subdivide is computed only once.
But most of the time we want variations
Glad it helped !
