The term,”trinity”, is not in the Bible and was brought up much later, but what is termed,”a high view of  Christology”, that is, that Christ is and was eternally divine and never just a man, is in both the old and new testaments,  the Gospels,  and Christ referred to Himself as such as recorded over 80 times in the Gospels.
For instance,  Jesus’s references of  Himself as the “Son of Man”. Islam uses this to refute the Christian claim that Christ is God in the flesh. They say,”Jesus called Himself son of man, so He clearly was not the Son of God.”
But what if “Son of Man” means something far more?
In Daniel 7 we read a prophecy –
13“I was watching in the night visions,
And behold, One like the Son of Man,
Coming with the clouds of heaven!
He came to the Ancient of Days,
And they brought Him near before Him.

14Then to Him was given dominion and glory and a kingdom,
That all peoples, nations, and languages should serve Him.
His dominion is an everlasting dominion,
Which shall not pass away,
And His kingdom the one
Which shall not be destroyed.”
(Daniel 7:13,14,The Bible )

Daniel basically said He looked like one of us! And in the beginning of creation God said ” Let us make man in our image” !

God used a plurality “our” description.

Daniel is in effect saying “He looks like one of us” , when in reality We look like Him! His image.

And look at the Gospel of Mark,  the oldest Gospel.

61But He kept silent and answered nothing. Again the high priest asked Him, saying to Him, “Are You the Christ, the Son of the Blessed?”

62Jesus said, “I am. And you will see the Son of Man sitting at the right hand of the Power, and coming with the clouds of heaven.”

63Then the high priest tore his clothes and said, “What further need do we have of witnesses?

64“You have heard the blasphemy! What do you think?” And they all condemned Him to be deserving of death.”
(The Gospel of Mark, 14:61-64,The Bible )
The Jews believe in one God as do the Christians. You believe in more of a demi-god, half man half god such as greek and Roman mythology beliefs.
We believe that when Christ was born that God embodied flesh , not that He created another god.
Since the term ” Trinity” had already been used in reference to the three ways man has experienced God, as His omnipresent Spirit, that He is our heavenly Father,  and that He also has eternally existed in a form “like the Son of Man” Jesus Christ.  This would also give a clue to the Genesis account of the creation of man “in Our image” command.

“Our” means God was in community with Himself in three personages embodied in one Being.

And “Son of Man” originated from Daniel’s vision when he described God’s form as “like the Son of Man” only we are actually the ones who where created by Him in His image.