Last month I discovered a new very basal form of U2, which I named U2[f], see here. Back then I knew of four samples belonging that subclade: two from Neolithic Hungary and two from modern Bulgaria. Since then I've found an additional example from Neolithic Britain and another from modern Picardy France.
Unlike U2[f], these newly discovered basal U5b subclades might actually be kind of popular. Also they might be geographic specific because all the representatives for each are from Eastern Europe.
mHG name: defining mutations.
U5b2a2[d]: 16192! 16217 16234 1117 3834 8941: Poland, Belarus, Volga Tatar.
U5b1b: 16192! 16147 3708 3849 6302: Slovakia, Livi Ukraine, Ryazan Oblast Russia, Smolensk Oblast Russia, Volga Mordovian.
U5b1a: 10373 204 207 235: Slovakia, Romania, Serbia, Russia.
In my database U5b2a2, which is the haplogroup I belong to, peaks in Poland, Belarus, and Austria. A large majority, maybe something like 70%, of U5b2a2 belongs to U5b2a2a or U5b2a2b. So the discovery of a new U5b2a2 subclade which extends from Poland to Russia is a pretty big deal. Based on the low diversity in U5b2a2 I suspect that it "expanded" in Central-East Europe during the Mesolithic or Neolithic. But that's really just pure speculation.
U5b1b might be a fairly important U5b subclade in Russia considering most examples of it are from Russia. There are two other popular U5b1b subclades near Russia; U5b1b2 in Finland and U5b1b1a in the Saami country.
Maybe U5b1b, U5b1b2, and U5b1b1a all descend from WHG heavy Neolithic foragers who were absorbed by new groups from the south like Corded Ware who first began to arrive in 2600 BC. An example of U5b1b1a has already been found in a Neolithic forager from Lithuania, see here.