Does anyone here have a tutorial on how to make a tree?

prefferably like the one on Big Buck Bunny on 0:23. Thanks in advanced.

in big buck bunny, they used an add-on called tree from curves. it is not available for current versions, but you can always use an old version, then export to a more recent version. hopefully without errors.
(edit) also there is the existing add on: sapling, which is pretty good. also there is a free software called ngplant which is good for modelling a variety of plants. it started out as a blender add on too. ( same as makehuman )

Another great add-on is SCA Tree Generator which gives you some great options.

Trees are an inherently difficult problem, because they are essentially 3d fractals which makes them crazy hard to UV unwrap.