I believe Adam wasn't with her at the tree, itself. I know the English Bible makes it sound like as if he was -- but I believe if he had been, then the two of them together would have resisted the temptation. I think if you read it in the original Hebrew that it also reads a bit differently.
As a secondary source, there was a female author in the last century whom said it this way:
In order to accomplish his work unperceived, Satan chose to employ as his medium the serpent--a disguise well adapted for his purpose of deception. The serpent was then one of the wisest and most beautiful creatures on the earth. It had wings, and while flying through the air presented an appearance of dazzling brightness, having the color and brilliancy of burnished gold. Resting in the rich-laden branches of the forbidden tree and regaling itself with the delicious fruit, it was an object to arrest the attention and delight the eye of the beholder. Thus in the garden of peace lurked the destroyer, watching for his prey. {PP 53.4}
The angels had cautioned Eve to beware of separating herself from her husband while occupied in their daily labor in the garden; with him she would be in less danger from temptation than if she were alone. But absorbed in her pleasing task, she unconsciously wandered from his side. On perceiving that she was alone, she felt an apprehension of danger, but dismissed her fears, deciding that she had sufficient wisdom and strength to discern evil and to withstand it. Unmindful of the angels' caution, she soon found herself gazing with mingled curiosity and admiration upon the forbidden tree. The fruit was very beautiful, and she questioned with herself why God had withheld it from them. Now was the tempter's opportunity. As if he were able to discern the workings of her mind, he addressed her: "Yea, hath God said, Ye shall not eat of every tree of the garden?" Eve was surprised and startled as she thus seemed to hear the echo of her thoughts. But the serpent continued, in a musical voice, with subtle praise of her surpassing loveliness; and his words were not displeasing. Instead of fleeing from the spot she lingered wonderingly to hear a serpent speak. Had she been addressed by a being like the angels, her fears would have been excited; but she had no thought that the fascinating serpent could become the medium of the fallen foe. {PP 53.5}
To the tempter's ensnaring question she replied: "We may eat of the fruit of the trees of the garden: but of the fruit of the tree which is in the midst of the garden, God hath said, Ye shall not eat of it, neither shall ye touch it, lest ye die. And the serpent said unto the woman, Ye shall not surely die: for God doth know that in the day ye eat thereof, then your eyes shall be opened, and ye shall be as gods, knowing good and evil." {PP 54.1}
...
The serpent plucked the fruit of the forbidden tree and placed it in the hands of the half-reluctant Eve. Then he reminded her of her own words, that God had forbidden them to touch it, lest they die. She would receive no more harm from eating the fruit, he declared, than from touching it. Perceiving no evil results from what she had done, Eve grew bolder. When she "saw that the tree was good for food, and that it was pleasant to the eyes, and a tree to be desired to make one wise, she took of the fruit thereof, and did eat." It was grateful to the taste, and as she ate, she seemed to feel a vivifying power, and imagined herself entering upon a higher state of existence. Without a fear she plucked and ate. And now, having herself transgressed, she became the agent of Satan in working the ruin of her husband. In a state of strange, unnatural excitement, with her hands filled with the forbidden fruit, she sought his presence, and related all that had occurred. {PP 55.3}
An expression of sadness came over the face of Adam. He appeared astonished and alarmed. To the words of Eve he replied that this must be the foe against whom they had been warned; and by the divine sentence she must die. In answer she urged him to eat, repeating the words of the serpent, that they should not surely die. She reasoned that this must be true, for she felt no evidence of God's displeasure, but on the contrary realized a delicious, exhilarating influence, thrilling every faculty with new life, such, she imagined, as inspired the heavenly messengers. {PP 56.1}
Adam understood that his companion had transgressed the command of God, disregarded the only prohibition laid upon them as a test of their fidelity and love. There was a terrible struggle in his mind. He mourned that he had permitted Eve to wander from his side. But now the deed was done; he must be separated from her whose society had been his joy. How could he have it thus? Adam had enjoyed the companionship of God and of holy angels. He had looked upon the glory of the Creator. He understood the high destiny opened to the human race should they remain faithful to God. Yet all these blessings were lost sight of in the fear of losing that one gift which in his eyes outvalued every other. Love, gratitude, loyalty to the Creator--all were overborne by love to Eve. She was a part of himself, and he could not endure the thought of separation. He did not realize that the same Infinite Power who had from the dust of the earth created him, a living, beautiful form, and had in love given him a companion, could supply her place. He resolved to share her fate; if she must die, he would die with her. After all, he reasoned, might not the words of the wise serpent be true? Eve was before him, as beautiful and apparently as innocent as before this act of disobedience. She expressed greater love for him than before. No sign of death appeared in her, and he decided to brave the consequences. He seized the fruit and quickly ate. {PP 56.2}