Clearly a modal tune, Madge on a Tree is in once-transposed Dorian (one flat in the signature with G as the final or tonic note). The climb to the final cadence is as clear as it could be, occupying the entire fourth phrase.
As a postscript to an earlier series on the clausula vera or cadenza perfetta in the sixteenth century, I have created a second part (at *) to show how naturally the 6-8 figure appears in a cadence with an ascending upper voice.
In this series of posts, basic information about the individual tunes is taken from Jeremy Barlow, ed., The Complete Country Dance Tunes from Playford's Dancing Master, 1651-ca.1728.