Answer: Cornus mas is a small tree, growing very slowly to about 20 feet with a nice, fairly regular natural shape. I would be very cautious about pruning it. Young trees often look gangly until they begin to mature. Here is a photo of a young Cornus mas, for example.
For more information about Cornus mas, see
If you eventually need to prune it, you could do so in late winter (temperature should be over 40 degrees) or in the spring right after it blooms.
Enjoy your new tree!
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