The Roboform Christmas trees were used by the Roboform to wreak havoc on Earth during the two invasions that took place on Christmas.
These remote-controlled trees could spin at extremely high speeds and rip apart anything in their path. They could also play songs such as "Jingle Bells". One of them nearly destroyed Jackie Tyler's flat. Another feature the trees had was to send out remote-controlled bombs disguised as baubles. (TV: The Christmas Invasion, The Runaway Bride) These baubles were used by the Tenth Doctor to decimate the Empress of the Racnoss and her children.
Like many other robots, they could be stopped using a sonic screwdriver. (TV: The Runaway Bride)