It could be a perennial and not a shrub or tree? I thought it looked similar to Baccharis halimifolia, but the leaves on that species have serration starting at the middle of the leaf and continuing up to the top. Your plant has leaves with their entire margins serrated. Oenothera was another guess, because of the leaves alternating which makes them look whorled. The closest Oenothera species had smooth leaf margins, which rules out Oenothera. Can I suggest that you feel the top and bottom leaf surfaces and add that to your descriptions? Compare your plant to Solidago radula, Rough Goldenrod. Try to remember to take a photo of a leaf face on, because venation is always crucial when identifying plants.

I wondered about a perennial but though I could see cut off woody stems at the base. Also very visible lenticels which looks shrubby.

Ilex vomitoria, Yaupon Holly?

Petioles and leaf bases don't match though. I'm out of ideas.

Jay's suggestion looks good. Another guess is some species of sedum, if it's "fleshy". Edit, looks woody down at the base, so not a sedum.

Baccharis biglovii looks like a match. The serrations span the entire leaf.

This appears to be a young privet (Ligustrum) plant. Privets are common in many regions and are often found in parks and along trails. They typically have serrated leaves like the one in your photo and can grow as shrubs or small trees.