Identify my apple tree
I am sending you a previous response that summarizes the difficulties in identifying one of the 7,500 known cultivars of apples, in addition to many wild varieties that you might have growing in your yard. If you can wait until the apple is ripe, you may have more color clues and could take an apple to a fruit grower at a farmer's market to see if this specialist can give you more help in identification.
"It is often very hard to identify particular apple varieties, especially if the tree is old. Many of our older trees are "wild" varieties with uncertain parentage. Furthermore apple seeds do not produce the same kind of apple that the parent tree is/was. Each seed in an apple will produce a different kind!
If your tree is younger and you can see the graft union (a bulge or knot of wood right at or slightly above the ground on the trunk) you can be sure that it is a named variety.
Sometimes an experienced apple grower will be able to make a good guess based on the size, shape and bark, leaves and fruit. Sometimes you can simply compare the look and taste of the apples to local varieties.
Here is a link to help you hunt down your apples. If nothing looks familiar you may simply have one of the many un-named hybrids.