Melchizedek in the Old Testament is spelled as Melchisedec in the New Testament.
Jesus was not Melchisedec, His priesthood was after the order of Melchisedec; in other words it was the same type of priesthood. That priesthood of Melchisedec didn't have a beginning of days; there is no record of his birth or death, and no family history was needed such as with the Aaronic priesthood requiring they be a Levite. There was no ending of days for Melchisedec's priesthood such as the 20 year duration of the Aaronic priesthood. Melchisedec was a king, and Jesus is a king; the earthly kingdom of Jerusalem was not the heavenly Jerusalem.
Hebrews 7:3 says Melchisedec was "made like unto the Son of God;" abideth a priest continually. Why would Melchisedec have to be made like unto the Son of God if He was the Son of God? We also are changed from glory to glory into the image of Christ, and our lives like unto the Son of God has no end.
Hebrews 7:1 "For this Melchisedec, king of Salem, priest of the Most High God, who met Abraham returning from the slaughter of the kings, and blessed him;"
"Salem" in the Hebrew tongue means "peace". Melchisedec was without a beginning, and there is no end to His life. He is supernatural. Genesis 14 gives us the record of Abraham going to battle with the kings of Sodom and Gomorrah, and three other kings, against Chedorlaomer, as well as kings that were his allies. Abraham joined with these men of Sodom because the people of Chedorlaomer and their allies had war and over ran Sodom and the cities surrounding it. Chedorlaomer took many people captive, in which Lot, Abraham's nephew and his family were part of the captives.
Ref. Genesis 14: Chedolaomer - 3540 Kedorla` omer (ked-or-law-o'-mer); of foreign origin; Kedorlaomer, an early Persian king: KJV-- Chedorlaomer.
After the battle there were many spoils from the lands that Abraham and his allied armies had conquered, and when the kings of Sodom and Gomorrah and their allies divided up the spoils of the battle, Abraham wanted nothing except that which was lots in the first place.
Genesis 14:16 "And he brought back all the goods, and also brought again his brother Lot, and his goods, and the women also, and the people."
Genesis 14:17 "And the king of Sodom went out to me him after his return from the slaughter of Chedorlaomer, and of the kings that were with him, at the valley of Shaveh, which is the king's dale."
Genesis 14:18 "(And Melchizedek king of Salem brought forth bread and wine: and he was the priest of the MOST HIGH GOD."
Genesis 14:19 "And He blessed him, and said, "Blessed be Abram of the MOST HIGH GOD, Possessor of heaven and earth."
Hebrews 7:2 "To whom also Abraham gave a tenth part of all: first being by interpretation king of righteousness, and after that also king of Salem, which is, King of peace;"
"A tenth part of all" is the "tithe", and this word comes from the Hebrew tongue.
Genesis 14:20 "And blessed be the MOST HIGH GOD, Which hath delivered thine enemies into thy hand." And he gave Him tithes of all.)"
"Melchizedec" [in the Greek is spelt "Melchisedec] is the priest of the "MOST HIGH GOD", and is also called "the King of Righteousness, the King of Peace [Salem] and the One deserving of the tithe."
Hebrews 7:3 "Without father, without mother, without descent, having neither beginning of days, nor end of life; but made like unto the Son of God; abideth a priest continually."
Our Heavenly Father is not natural, but He is a supernatural entity. He had no pedigree showing His authority, he just showed up before Abraham, yet Abraham knew Him, and that the tithe was deserving to Him.
Melchisedec was made like the Son of God, Jesus Christ. Remember this giving of the tithe took place almost two thousand years before the birth of Jesus, from the womb of the Virgin Mary. The reason that Melchisedec looked like the Son of God, was that He was the Son of God. This should not be a problem of understanding that this King of peace and righteousness was Christ, because there is only one that will fit this description in the entire Bible.