Your friend's daughter should first make a police report of the incident. If the at-fault pick up driver stopped hopefully she was able to get his insurance information besides just his name. If not she should contact the driver to get their insurance information and then contact that insurance company to make a claim.

The driver whose vehicle was struck by the Christmas tree as it fell out of the pickup should also inform her own insurance company of the incident. This way if the pickup driver does not have insurance or she is unable to get his insurance information in a timely manner she can put a claim in against her collision coverage. Collision covers a vehicle when it is hit or is hit by another vehicle or object.