Most of the dictionaries that include overtread as a verb have sourced it from the 1913 Webster's Unabridged, which lists a lot of very ancient and obscure words, many of them too rare even for our rare list.
However dictionary.com has it as a noun, at the end of the entry for tread. No definition is given, but it may be something you can have on a tyre.
In any case, the verb overtread is to be found in the Shorter Oxford, which I feel is a good guide for our purposes. They say it's now rare, and has the meanings "Tread over, trample under foot; fig. oppress, subdue."
Most of the small number of examples I found are in little-known poetry from the 19th century or earlier. But ensiform gives us a link to a political article, and the OED gives an example from sporting journalism: "He helped out without ever overtreading the line between assistant and head coach." (1999, Morning Call, Allentown Pa.)
I'll add it as a rare word. The only inflected form short enough for us is the past tense overtrod. I'll add that too.