Of course you are right! But as I understood the article, the treatment difference occured during the first phase, association between character and meaning. They observed that those character-meaning pairs that got repeated more often during the first phase have been remembered more often in the second phase (as part of two-character combinations).

It's also book in Kanji, and I've always thought it looks more like a book with its leaves hanging open - even though the pictogram is indeed a tree.

You may be thinking of 本 :)

It actually has a much more complicated and varied etymology than that of 'tree'.

http://www.chineseetymology.org/CharacterEtymology.aspx?subm...

The Heisig method is very good at getting you to be able to remember the differences between characters, in particular how to write them. (To keep it on topic...) it is based on building up the characters from previously learned components ("radicals"). It also builds on your existing knowledge of English because you learn the radicals and characters with English keywords. The idea is to learn the characters in English first, so that you'll have that as a base of knowledge to learn the actual language.

[1] a good intro: http://akitajet.com/wiki/Heisig_Method if you want to try the method I would suggest picking up Remembering the Kanji volume I and then utilizing http://kanji.koohii.com for the mnemonic "stories" and to practice with their spaced repetition method.