I tried to do this many years ago. My data represented the number of
students enrolled at a college, split by gender and by age - it
occurred to me that by plotting male as -ve and femail as +ve and age
(in 5-year bands) on the y-axis, and by colouring the "branches" (on a
bar-graph) green, then the result may look like a xmas tree (it was in
November/December that I was doing this, so there was the seasonal
element). In the end it didn't look too much like a Christmas tree as
it was much broader in the lower age bands (19-24, 25-29), but everyone
referred to them as Pete's Xmas tree graphs.
Hope this helps you.
Pete