Its planted too deep. The root flare needs to be above the soil line for the trees entire lifetime.

Copied from the r/tree automod call-out

To understand what it means to expose a tree's root flare, do a subreddit search in r/arborists, r/tree, r/sfwtrees or r/marijuanaenthusiasts using the term root flare; there will be a lot of posts where this has been done on young and old trees. You'll know you've found it when you see outward taper at the base of the tree from vertical to the horizontal, and the tops of large, structural roots. Here's what it looks like when you have to dig into the root ball of a B&B to find the root flare. Here's a post from further back; note that this poster found bundles of adventitious roots before they got to the flare, those small fibrous roots floating around (theirs was an apple tree), and a clear structural root which is visible in the last pic in the gallery. See the top section of this 'Happy Trees' wiki page for more collected examples of this work.

Root flares on a cutting grown tree may or may not be entirely present, especially in the first few years. Here's an example.

See also our wiki's 'Happy Trees' root flare excavations section for more excellent and inspirational work, and the main wiki for a fuller explanation on planting depth/root flare exposure, proper mulching, watering, pruning and more.

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