Eupatorium purpureum

Thank you for your response! Flower buds are still white. Maybe this is a white flower variety or turns pinkish later.

It may be a Eupatorium, but not E. purpureum which has whorled leaves. Perhaps Eupatorium serotinum.

Another to consider is White Snakeroot, Ageratina altissima. (formerly named Eupatorium rugosum)

Here is a link that might be useful: White Snakeroot

Thank you all for the responses! I'll see how it looks like when it fully blooms.