Procedural Wood Shader : Burr Elm
Why the aspect ratio looks wrong?
Dont forget to always apply the new scale of a modified object (ctrl + A) in order of having X, Y and Z scale to 1 from the transform info panel (N shortcut).
How do I add this material in my blender file?
In your file, click File > Append and then navigate to the NodeTree folder and click on Burr Elm. This will result on adding the node group on the library.