Pashtuns before Islam: A detail in “Ajaib al-Makhluqat” of Muhammad al-Tusi (written in 1160-1167 AD) might be a reference to pre-Islamic Pashtuns. According to it, there was a large tree with circumference of seventeen arsh (?) in a Tamarisk forest of the Afghan (i.e. Pashtun country). That particular tree was known as ‘the tree of Brahman’ (درخت برهمن) and Pashtuns would prostrate before it.
1- It might be that those Pashtuns were followers of Buddhism or some other religion. That tree could be the ‘Budhi’ tree of Buddhism, incorrectly referred to as the Brahman tree by Al-Tusi. The author of Hadud al-Alam and Al-Beruni alludes to the fact that pre-Islamic Pashtuns were not Hindus.
2-It is also possible that it was just a rumour which reached the ears of Al-Tusi. After all his book Ajaib al-Makhulqat contains details about fictitious and mythical creatures. It might be that there was a grave of a Muslim saint besides the tree or the tree was associated with that saint and the superstitious Pashtuns had started venerating the tree. There is another similar instance in history in which Shaikh Qasim, a Pashtun saint from Peshawar in 16th century, made a tree in Palosi village, a ziarat for his followers. Thousands of people started visiting that tree and would pray for their wishes there. It was cut by the orders of Mirza Shadman (a Mughal noble of Mirza Hakim, the ruler of Kabul at that time). But the tree grew again. Eventually the followers of Syed Isa Biloti cut the very roots of the tree and the tree never grew again but the site of that tree continued to be visited by the pilgrims. This information is provided by Asrar al-Afaghina, written in 1604 AD by a disciple of Shaikh Qasim (a Khalil Afghan).