Both disobeyed fundamental principles that are extremely important to god. It is important to remember that although the first human couple was given free will, God also told them that he was still the one who puts the rules, thus he placed the tree. The bible doesn't say that the tree had any special features by itself, it was more a symbol of God's authority to decide what is good or wrong, of the limits that he had placed to their freedom. Adan thought that he could decide by himself and he despised God's authority.
The fallen angels were created by God as spiritual beings, they also had free will. By making themselves physical forms (the complete opposite of God's purpose) they also despised God's authority to decide what is good, and what is wrong.
I think the connection lies on pride, both the angels and man showed disobedience and pride to not follow God on his rules and laws. They displayed pride in their actions that were unacceptable to God. I hope this answered your question.
