Our apple tree

It is actually not a tree yet but a sapling. My niece planted it from a seed that she had experimented. When the seed germinated and produced leaves she was happy to inform me. On Christmas day the other year my niece gave the seedling to me which was planted in a small plastic pot.

I nurtured the seedling that the 4 leaves started to multiply. After some months the seedling has become a sapling with many branches. Now it is more than a year old but the branches are thin and even the main stalk is thin. I wonder.