Berkshire Hathaway Inc (BRK.B)

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And what does that 2X S&P fund hold? A whole bunch of swaps. Derivatives. Some of them foreign.

Leveraged ETFs, such as SSO, can be dangerous for longterm investing:

"While these types of leveraged and inverse ETFs may help
traders capitalize on short-term moves, investors should
be aware of the risks and potential divergence between these
geared products and their underlying assets over the long
haul and during periods of heightened volatility."

http://www.investopedia.com/stock-analysis/2009/the-painful-truth-about-leveraged-etfs-sds-sso-uyg-skf0710.aspx

https://www.etftrends.com/2016/05/navigating-risks-of-leveraged-inverse-etf-play/