Not without photos of the fruit, tree, trunk, etc. You are giving us conflicting information, so I'm wondering if perhaps your tree has a branch or two of rootstock that has grown up from below the graft line, and that's the bitter fruit. And, the other, sweet fruits are actually the cultivar. Please post up photos of both sections of the tree - sweet and bitter - and give us nice clear photos of the leaves of both of those branches. Plus, cut the fruits in half, as well as whole fruits, and let us know which are the sweet ones and which are the bitter ones.

Patty S.