A fruit tree sprouted in our back yard. We thought it was an avocado tree by the leaves and the small roundish dark green fruit that came out. Eventually the fruit has turned from nubby to softer flesh, lighter green and then yellow. If you cut one open, it has small seed clusters the size and color of sesame seeds and it's pinkish inside. Smells like a grapefruit almost. Does anyone have any ideas what it is? The leaves are about 5-6 inches long, single not clusters..look almost identical to avocado leaves.