first off, make posts about getting help, in the HELP forum. your tutorials is made for tutorials obviously.
where to start?
well first off, do you know about the random expression?
random(VALUE) it a random number between 0 and what you input. remember that if you put a number, its not going to ever return the number you gave, but instead integer every number below it including 0. so random(10) would give you 0,1,2,3,4,5,6,7,8,9 but never 10.
after you know about that expression your gonna need an object for branches, that you spawn and then at its end you spawn more branches, always setting theyre length and angle to a random value.
then youd need some cutoff point and a leaf spawner. not gonna go into anymore detail you figure it out!