The US treasury is about $20 Trillion, divided by 20 m bitcoin, that is $1m for each bitcoin.
I'm not sure what you mean by "the US treasury is about $20 trillion", but the St. Louis Adjusted Monetary Base is about $4 trillion, so $4 trillion divided by 20 million bitcoins is $200,000 per bitcoin.
The value of a bitcoin will exceed $200,000 only if all the dollars are replaced by bitcoins (assuming FRB at current levels).
Bitcoin market cap is very misused term. The reality is if you use 100 million USD and buy Bitcoins, you might longterm increase the Bitcoin market cap by Billion of USD. This means you can have stable market value $200,000 per Bitcoin without the need to use $4 trillion USD to buy Bitcoins...