Catalog › Birch tar oil rectified + Iso E Super
These two appear together in 4 of the accords published to the PerfuMate community. That is a record of two materials used together in real formulations, and it is only that: a record of use, not a recommendation engine. The accords are listed below so the evidence can be read.
They share no olfactive family: Birch tar oil rectified is filed under Smoky, Leather, Resinous, Sweet and Iso E Super under Woody, Amber. What joins them here is use, not classification.
Each accord is a formula published to the PerfuMate community, and these are PerfuMate's own reference accords rather than third-party work. The figures are each material's share of the concentrate in that accord.