Investors piled into America's hottest investment product following Trump's election win

Donald Trump's surprise US election win led to a stock market rally, with the S&P surging 3.8% last week and the Dow Jones Industrial Average closing at an all time high on Monday.

As the markets embraced Trump's victory, Bank of America Merril Lynch saw its clients buy $2.3 billion worth of US stocks last week, according to a note circulated on Tuesday.

This was the largest weekly net buy from BAML clients in 10 months, and was comprised almost entirely by ETFs.

ETFs, or exchange traded funds, are one of the fastest-growing types of investment vehicles in the markets now. Because of generally lower costs and higher liquidity than mutual funds, ETFs have gone from $230 billion in assets to around $4 trillion over the past 10 years. And it doesn't seem to be slowing down.

Last week, ETFs saw their biggest inflows since late 2014, as hedge funds, private clients and institutional clients piled in.

After ETFs, tech stocks saw the next large inflows followed by staples and financial stocks. Clients were net sellers of everything else, led by the healthcare and industrials sectors.