Chris Trapani and Ryan Iwanaga, owners of Silicon Valley-based Christie's International Real Estate Sereno, are heading the expansion. Their company is already the largest independent brokerage firm in Northern California, with offices throughout the Peninsula, Silicon Valley, East Bay, Santa Cruz, Tahoe, the Sierra Foothills, and the Central Coast. The new offices will do business as Christie's International Real Estate San Francisco | Marin | Wine Country. Trapani, Iwanaga, and Christie's International Real Estate have carefully chosen a founding group of REALTORS® representing the highest standards in San Francisco's luxury market.