Ways to invest in Bitcoin
1- Direct ownership
2- Mining hardware
3- Qualified investors fund- Second Market
4- Qualified investors - angel investing in service and equipment providers
5- ETF- Winklevii (future)
6- Closed end funds as discussed here (future)
7- REIT with 25 % in BTC (future)
8- Trusts, do any exist yet?
There are many other possibilities (all future):
Unit Investment Trust - or like vehicle
IPO
Commodity fund (? Who knows - depends on how BTC is categorized)
Charitable income trust (wealthy person donates BTC to his own charity, can get current deduction for full amount and can provide income from the trust to beneficiaries)
Mutual Fund focused on BTC
Many many variations of types of funds which are publicly traded
DPO, direct public offering
Different types of ETFs
Hedge funds invested in BTC
Separately managed accounts focused on BTC
VC fund focused on BTC related companies
Several different non US vehicles.
It's also not as hard as some May think to invent a new investment type --- or, better yet, to re-invent or revise some older vehicle type for BTC.