Celtic word for "tree"

I subscribe to the magazine "Parabola."  In an article entitled "The
Celtic Tree of Life" by Mara Freeman occurs the following
statement: "That most magical of Celtic trees, the oak, derives its
Gaelic name (Old Irish "daur", Welsh "derw") from the Sanskrit
word "duir," which gives us "door."

There are two PIE roots: *deru (with variations) which is the origin
of the English "tree," and *dhwer (with variations) which is the
origin of the English "door."  I believe the author of the above
statement is wrong in deriving the Gaelic word from the PIE root for
door.

Any comments?

Charlie

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