In yeshiva, I learned that the ten Sphirot are a part of the essence of G-d, and that some of the Mekubalim direct different part of Shmone Esre to different Sphirot. They (the Mekubalim) also believe that some of the Sphirot pray to Ein Sof. Some even go as far as saying that Ein Sof isn't the one that created the world since He is eternal and transcendent; but, that it was instead created by one of the Sphirot.
How does the above not contradict the unity of G-d? And, why is it any different from the idea of the Christian Trinity?