Modern20 doesn't usually have feat trees. Most feats have at most one prerequisite feat. This is part of the way the game makes generating characters easier.
Voyage of Discovery's magic feats though, are going to qualify as feat trees, with 2+ feats required for advanced magics.
To Joey, yeah, I think most of the time feat trees are not necessary. They just slow down character generation, especially for the GM creating higher level NPCs.
For a spellcaster though, I think a little more complexity is ok.