Hi Aussietim
I also have been trying to verify the IGI entries for Griffiths Tree and Elizabeth King for some time, without any success. Until I came across other Northiam Tree families in the England censuses (often indexed as Free), I was beginning to suspect that he had changed his name.
I am not certain of the accuracy of Elizabeth Ashdown as his mother. The only place I have seen mention of Elizabeth Ashdown is on Griffess Trees' death certificate, so it could be fuzzy memory on the part of his wife - particuarly as the Tree surname is not mentioned, just the mother's maiden(?) name. Have you seen Elizabeth Ashdown mentioned on any other documentation?
There is an entry in the Burial Parish Records on FindMyPast for William Tree, age 40, about 1812 in Northiam. This could be the father of Griffiths Tree, particularly with Griffiths's first son was named William.
I am hoping that eventually the Northiam information will be indexed and available on the Internet, so I keep searching. I have written to the Sussex Family History Society requesting a lookup of the marriage of Griffiths Tree, and will post any info I receive.
Regards
Judy