I assume from your link that you are interested in the Barnabas Bidwell portrait at the top left of the article. Under the photo is a caption that says, "Source: Courtesy of Wikimedia Commons". If you click on that link it will take you to a page describing the photo and its status. In this case, the photo is considered to be in the public domain and free to re-use. If you click the Download icon at the top, it will give you the suggested Attribution.
See this link to Wikimedia Commons:Simple media reuse guide for an easier to understand discussion of Wikimedia Commons images. Specifically note "All media files on Wikimedia Commons can be used by anyone, including commercially and each media file has information about which license it uses. The most common licenses used are created by Creative Commons which require the author to be credited."
So yes, you can use this image on Wikitree and give the source appropriate attribution per the Honor Code.