New to Apple Trees

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5 year old buck +
New to apple trees and have search site to see what (if anything) this could be but thought a picture might be easier.

Anything to be concerned about with the coloring below? Planted 6 trees last spring and this the only one with this coloring around the bottom.

Apple Tree Color.jpg

Top of the tree looks to be growing fine.

Apple Tree Color Top.jpg
 
Nothing that looks like any disease I know of. Almost looks like it was wrapped or shaded by something else to that line.
 
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