Ah... I knew I recognised the criss-cross tree from somewhere.  It's hardly surprising that the song was difficult to find; it is taken from the folklorist Ruth L. Tongue's book The Chime Child, or Somerset Singers (Routledge and Kegan Paul, 1967), and described by her as "Sung by Mrs. Cordelia Cooper above Ashley Coombe, August 1943.  Composed by an Exmoor Gipsy, probably a Lock, in the 1920's or earlier".

Ms. Tongue describes her first meeting with Mrs. Cooper, a Romany resident on Exmoor between 1942 and 1943, at Worthy Wood near Porlock (hence the name of the song).  There is another song from Mrs. Cooper already in the forum, with tune in abc and miditext formats:  The Broom Squire's Bird Song.

Now the caveat as to the songs in this book.  With (I think) one exception only, none of them have ever been found anywhere else, and many of them, and their tunes, have oddly similar structures which are not generally found in tradition.  Additionally, Ms. Tongue's sources are given pseudonyms, and cannot be identified.  Many people have come to the conclusion that the book is at least in part a work of fiction, and that the songs were made by Ms. Tongue herself.  However that may be (and there is no way of knowing for sure), some of them are very powerful pieces; people should be wary of describing them as "traditional", though, at least without referring specifically to the printed source, as there is a good chance that they are nothing of the kind.

I have made midis of the tune as given in the book; until they appear at the  Mudcat Midi Pages,  they can be heard via the  South Riding Folk Network  site:

The Worthy Wood Carol
The Worthy Wood Carol  [Tune variation in bar 6].

The tunes were transcribed from a tape recording of Ms. Tongue and "a friend", so the variation may be hers rather than her (putative) source's.  There are several other songs from Ms. Tongue in the Forum:

On Sedgemoor (The Marsh Fever)   -With tune; from The Chime Child.
The Broomsquire's Bird Song   -With tune; from The Chime Child.
The Quaker's Wife  -With tune from another source.  Text from The Quaker's Wife and other Somerset Folk Songs, Ruth Tongue and Felton Rapley (Chappell & Co., 1965).
The Green Lady  -With tune; from The Chime Child.
Three Danish Galleys  -With tune; from The Chime Child.