Help with Seedling not growing

Gday All. A few weeks ago I planted some seeds which had grown roots in an apple. One of them came up nicely and has got its first leaves while this one has seemed to push the seed out, restricting the growth. It has been like this for over a week and the plant seems to be healthy, but it doesn’t seem to be growing any further in a hurry.

Just wondering if you have any idea what exactly is happening, how(/if) I can fix it and how to avoid this happening in the future?