Question: **Location**: Northern China  

**Height**: I guess it's over 15m, about 20m.  

**Note**: All leaves would fall out in the winter.

[![The leaf](https://i.stack.imgur.com/NaNLy.jpg)](https://i.stack.imgur.com/NaNLy.jpg)
[![The trunk and the bark](https://i.stack.imgur.com/c5TA5.jpg)](https://i.stack.imgur.com/c5TA5.jpg)

Answer: 
Thanks! @Bamboo, @stormy, @Stephie  

I have known it.  

It's **Populus alba**.  

See here → [Wiki](https://en.wikipedia.org/wiki/Populus_alba)
I think this is Alnus rubra or Red Alder. A very tough tree.