I would also remove it, if you are in many parts of the US, the Gala apple trees are very disease prone. Some of them, will develop splits in the trunk down the road as well, that require removing the tree or constant treatment. If you do remove it, unless you are very attached to Gala's, I would purchase a different type of apple, unless you live in say the Yakima or Hood River Valley or similar climes. There are many disease resistant dwarf apple trees now available that you might consider. Check out the catalog from Raintree Nursery, it contains really good descriptions of many of the available dwarf apple varieties and their size range and bloom time. Note, the even on ultra dwarf stock some apple will still get 15 or more feet tall, while some types of apples on m-26 will top out at 6-8'. If you replace it, make sure to get m-26 or an even more dwarfing stock. Dwarf is a very relative term in the US. Many people I know have purchased dwarf trees that now look like semi-dwarfs after 6 years, because they didn't check on the dwarfing stock used.