The letter Bet stands for a house (bayit), and it is written, "By wisdom a house is built. -Proverbs 24:3". Bet also stands for a bracha, a blessing, and by blessing and praising God and others, we draw wisdom to ourselves. Also, since the topmost sefirah, Keter, means "crown", this passage informs us that every part of the Tree of Life becomes the crown for a Tree within the Tree. Iteration and repetition lead from simplicity to infinite detail.
(Here's that picture just one more time!)
