We learn from the Torah that Akedat Yitzhok took place on the mountain of Moriah. We also know that Malki-Tzedek came to Avraham Avinu, bringing bread and wine. (Bereishit 14:18) Rashi brings the rabbinic tradition that Malki-Tzedek was Shem, the son of Noah. The Torah tells us he lived in Shalem, which is identified by the rabbis as Jerusalem.
In the ancient times people have built their altars on the bamoth, or "high places". So it's very likely that the Shem's altar was on the holy mountain rather than on the plain (I think it is not a coincidence that he lived in Jerusalem). But we read nothing about Shem/Malki-Tzedek helping Avraham in building his altar on the very same mountain where we expect to see the altar of king/priest of Hashem. And it is strange to build your altar on the holy place on the very same place where king/priest is living, to whom you just gave tithes.
I'm just curious if any of the sages comment on that?