CHATTANOOGA, Tenn. — A school bus driver who authorities say was speeding along a narrow, winding road when he wrapped his vehicle around a tree was arrested and charged with vehicular homicide in the deaths of five children.The wreck Monday afternoon plunged the city of Chattanooga into mourning, with parents stricken by the news and people lining up to donate blood.“The most unnatural thing in the world is for a parent to mourn the loss of a child,” Mayor Andy Berke said. “There are no words that can bring comfort to a mother or a father. So today, the city is praying for these families.”Police said Johnthony Walker, 24, was driving well over the posted 30 mph limit when he lost control of the bus. He was jailed on $107,500 bail for a court appearance Nov. 29 on charges that also included reckless driving and reckless endangerment.Thirty-five Woodmore Elementary School students from kindergarten through fifth grade were aboard when the bus flipped onto its side and hit a tree. No other vehicle was involved.