improve slow-tree output

example:

![j7_dznbhuzu7bh4zfzrz64oh2zz2thofgoukopxyba8](https://cloud.githubusercontent.com/assets/1377/3487791/36671cc2-04a3-11e4-8cdd-c83552fbdeaa.png)


We may want to improve this more, but this already provides more context.