myTree: length diff: d angle: a
length > 2
ifTrue: [
self go: length.
self turnLeft: a.
self myTree: length-d diff: d angle: a.
self turnRight: a*2.
self myTree: length-d diff: d angle: a.
self turnLeft: a.
self turnLeft: 180.
self go: length.
self turnLeft: 180.
].