It is not at once apparent why the book is styled an  almanac,  but that is  there is no other book I know of that contains as much diverse information about American writers as this one.
( ( ( ( ( It ( ( ( is not ) ( ( at once ) apparent ) ) ( why ( ( the book ) ( is ( styled ( an almanac ) ) ) ) ) ) ) , ) but ) ( ( that is ) ( there ( is ( ( no ( other book ) ) ( I ( know ( of ( that ( ( contains ( as ( ( ( much diverse ) information ) ( about ( American writers ) ) ) ) ) ( as ( this one ) ) ) ) ) ) ) ) ) ) ) ) . )
(ROOT (S (S (NP (PRP It)) (VP (VBZ is) (RB not) (ADJP (ADVP (IN at) (RB once)) (JJ apparent)) (SBAR (WHADVP (WRB why)) (S (NP (DT the) (NN book)) (VP (VBZ is) (VP (VBN styled) (NP (DT an) (NN almanac)))))))) (, ,) (CC but) (S (INTJ (DT that) (VBZ is)) (NP (EX there)) (VP (VBZ is) (NP (NP (DT no) (JJ other) (NN book)) (SBAR (S (NP (PRP I)) (VP (VBP know) (PP (IN of) (SBAR (WHNP (WDT that)) (S (VP (VBZ contains) (PP (IN as) (NP (NP (ADJP (RB much) (JJ diverse)) (NN information)) (PP (IN about) (NP (JJ American) (NNS writers))))) (PP (IN as) (NP (DT this) (NN one))))))))))))) (. .)))
It's not obvious why the book is like an almanac but it contains more diverse information on American writers than any other book. 
( ( ( ( It ( ( ( 's not ) obvious ) ( why ( ( the book ) ( is ( like ( an almanac ) ) ) ) ) ) ) but ) ( it ( ( contains ( ( more diverse ) information ) ) ( on ( ( American writers ) ( than ( any ( other book ) ) ) ) ) ) ) ) . )
(ROOT (S (S (NP (PRP It)) (VP (VBZ 's) (RB not) (ADJP (JJ obvious)) (SBAR (WHADVP (WRB why)) (S (NP (DT the) (NN book)) (VP (VBZ is) (PP (IN like) (NP (DT an) (NN almanac)))))))) (CC but) (S (NP (PRP it)) (VP (VBZ contains) (NP (ADJP (RBR more) (JJ diverse)) (NN information)) (PP (IN on) (NP (NP (JJ American) (NNS writers)) (PP (IN than) (NP (DT any) (JJ other) (NN book))))))) (. .)))