Proposal: improve the Data.Tree API

[Henning Thielemann]

On Wed, 31 Dec 2014, João Cristóvão wrote:

> For the record, nevertheless, I was moving along with the separate 
> Tree/Forest modules to avoid further bikeshedding, but to be honest I 
> don't really see a big advantage - if your using one, you most probably 
> will also need to use the other, so why two imports?

What is bad about two imports?