Discount stock broker Upstox on October 3 said it has concluded a buyback of 5% of Ratan Tata's holdings in the company. Tata had bought around 1.33% stake in Upstox in 2016. "Mr Tata's stake in Upstox has registered a whopping 23,000% return on original investment made in 2016, based on our last round valuation of $3.5 billion," Upstox said.