Maple, possibly red maple. Full sun, trunk gets planted only as deep as the roots. Planting deeper will damage the trunk. Maples do better when planted more shallow than most plants. Are there 1 or 2 trees in the pot? If 1 tree with 2 trunks it might do better if you trim the smaller part back to the root zone. Or is the thicker stalk a bamboo support? If it's a support that small of a tree really doesn't need it. The roots grow stronger if a small tree isn't staked or supported.