Hi Denis,

the French name is "loupe". "loupe" is already described in the French
academy dictionnary (1798) as an excrescence (not limited to trees)
Sometimes, when the burl is caused by the successive trimming of
branches (for example in plane), it is called "boule" (ball).
I've never heard the word "bourle", but it is very close from
"bourrelet" (draught in UK eng, draft in US !), so it's quite
possible.
hth,

Pascal
Grenoble, France