MicroStrategy Inc. is making waves in the $310 billion market for US convertible bonds. Thanks to Bitcoin's impressive rise, the company is driving returns in this space.

A Bloomberg index, which tracks 500 convertible US debt securities, is on track for its best month this year. Remarkably, MicroStrategy is responsible for nearly 25% of that growth.

The company's bonds that mature in February 2027 have jumped 60 cents on the dollar this November. This surge puts them on course for their best monthly performance since they were issued back in 2021.

However, investors are raising concerns about concentration risk in the convertible bond market. It's a situation worth keeping an eye on.