One possible version：
Dear Sure,
I’m Li Hua, one of your students in China. It’s almost a month since you left us. We all miss you and are very grateful for what you did for us.
We are busy as usual. We had an English speech contest the other day. I won the first prize! This again reminds me of all your kind help. Do you still remember the trees we planted together on the hill behind the school? Yesterday, we went there and watered them. The tree you planted yourself is growing well, and the whole class decided to name it Sue Wood. Will you come back to see Sue Wood?
How is everything with you lately? We hope to know more about you and your American students. Hope to keep in close touch.
All the best
Li Hua
略