beginfig(1)

u := 2cm;
offset := 120;

def drawgreen(expr p, linethick) =
  draw p withpen pencircle scaled linethick withcolor 0.5green
enddef;

def drawpink(expr p, linethick) =
  draw p withpen pencircle scaled linethick withcolor red+0.6green+0.6blue
enddef;

vardef tree(expr A, B, n, size) =
  save C, D, thick;
  pair C, D;
  thick := size;
  C := 0.8[B, A rotatedaround(B, offset+uniformdeviate(60))];
  D := 0.8[B, A rotatedaround(B, -offset-uniformdeviate(60))];
  if n > 0:
    drawgreen(A--B, thick);
    thick := 0.7*thick;
    tree(B, C, n-1, thick);
    tree(B, D, n-1, thick);
  else:
    drawgreen(A--B,thick);
    thick := 0.7*thick;
    drawpink(B--C, thick);
    drawpink(B--D, thick);
  fi;
enddef;

tree((0,0), (0,u), 10, 3mm);
endfig;
bye