(a) Rashi d.h. "sh'onin' says we complete Hallel and say the Hagadah. why does Rashi first mention Hallel, which as said after "magid"?
(b) Tosfos d.h. "mah moro" answers that just as matzoh is a species of vegetable/"zro'im," so too, moror cannot be a bitter olive, because it is a tree fruit.
The gemara Sanhedrin perek chelek says that the tree from which Odom ate was "chitoh," so we see that chitim is also considered from a tree.
ZAF, Toronto - Canada
(a) Saying Hallel during the Shechting of the Korban Pesach in the time of the Beis ha'Mikdash started well before Magid. Rashi therefore says that we complete something that we already started on Erev Pesach, namely Hallel (see 64a), and also have a special Mitzvah of Magid when we have (the obligation of) Matzah.
(b) This is only one opinion, that of Rebbi Yehudah in Berachos (40a), upon whom many opinions argue.
Additionally, as the Gemara itself points out in Berachos (ibid.) even according to Rebbi Yehudah one does not say a Borei Pri ha'Eitz on Chitah, as it cannot be called a Pri ha'Eitz. Tosfos could therefore still say that just as Matzah is a Pri ha'Adamah, so too Maror must be a Pri ha'Adamah.
Kvod hoRav, nR"u
(a) We are discussing the matzoh she'onim olov. It need not be present at the sh'chitas haPesach, so how is this an answer?
(b) Chitoh being eitz- Your Additional answer is very satisfactory, but your first answer - I am fully aware that there are numerous other opinions that the eitz hadaas was another item, but those who offer other opinions do not do so because they posit that chitoh is not an eitz, so it seems that they agree to that point, just they say, for example, it was t'einoh because the bgodim were of the same species as the sin, etc.
(a) You are emphasizing the Matzah in regards to Hallel. The answer above is that when Rashi mentioned "*v'Gomrin* Alav Es ha'Hallel," he was taking into account that Hallel had already started to be said Erev Pesach regardless of the fact that one does not yet need to eat Matzah. Just as if someone finishes a job, it does not necessarily mean that he necessarily started it, so too the phrase "and we finish on it (Matzah) Hallel" leaves room to understand that the saying of Hallel started even before the actual Zeman of Matzah she'Onin Alav.
(b) A careful reading of the Gemara in Berachos (40a) does not seem to support your understanding of the other opinions. The Gemara there asks why the Mishnah deemed it necessary to say that one is not Yotzei if he says a "Borei Pri ha'Eitz" on Peiros ha'Aretz. It is obvious! The Gemara concludes that it is only necessary because one would think otherwise according to Rebbi Yehudah's opinion that Chitah was the "fruit" of the Eitz ha'Da'as, unlike the other opinions which the Gemara proceeds to quote. According to your understanding of the Gemara, *everyone* should think that, not just Rebbi Yehudah, as everyone agrees it is an Eitz! It therefore follows that they hold it is simply not an Eitz.