One school of thought in regards to the Indo-European languages suggests that they exhibit a “rake-like” phylogeny. That is, they expanded rapidly and simultaneously in all directions. Aside from the connection between Iranian and Indic branches, there’s no obvious connection across the others (satem-centum distinction aside).
In The Indo-European homeland: introducing the problem Thomas Olander produces the above chart. It is not rake-like. What jumped out at me are correspondences/connections to Y chromosomes.
The two main branches of R1a1a are found in the Indo-Iranian and Slavic branches of the Indo-European family. The coalescence is ~5800 years ago.
There are some suggestions that Italic and Celtic form a branch. As it happens, Italy, Celtic and ancient Celtic regions of Europe have very high frequencies of R1b.
What about the Tocharians? The Afanesievo people were basically Yamnaya-east. They had a lot of R1b. Today, a small minority of Uyghurs have R1b. Far more have R1a. But, I think it is important to note that the Tarim basin was mostly Iranian in the southern and western regions, and Tocharian in the north and east. The prevalence of R1a may simply be a function of the nature of the sampling.