Complex sentence: A Mutual insurance company is an insurance company which has no shareholders but instead is owned entirely by its policyholders: this ownership either extends to all its policyholders or is restricted to certain classes of policyholders.
Split into simpler sentences: A Mutual insurance company is an insurance company which has no shareholders but instead is owned entirely by its policyholders. This ownership either extends to all its policyholders or is restricted to certain classes of policyholders.