I have a 18" maple seedling that I transplanted last summer from my old
home to my new home. It's from a fantastic maple that covered the
entire back yard, & the seedling started naturally under my picnic
table. The original tree is about 40' tall. Zone 4.

However, it's a Y shaped seedling. My questions a

1) Do I let it continue to grow as a Y, or do I remove one of the
branches?
2) If I remove one of the branches, what season, & how old should the
tree be? Will the remaining branch grow vertically, or continue
growing at an angle?