Why did the weeping willow weep?

Question

In each sentence the name of a tree is hidden. The willow is hiding in the first sentence. Can you find the others?

1. I will owe you a favor if you drive me to the airport.
2. I am afraid of going up in elevators.
3. Drinking cocoa keeps me warm on long winter nights.
4. I hope the map leads us to buried treasure.
5. "Eat another bonbon," said our charming hostess.
6. Nepal may be the most interesting place I have ever visited.
7. Remember to fold the map, please.
8. I feel many lumps in this mattress.
9. Word processing is not as useful as pens and paper for creative brainstorming.