Have you learned to access the pre-made presets by pressing the alt button while clicking on the tree icon? A dropdown menu will appear with quite a few presets. Here's a lovely willow recipe I copied from Aldaron. It goes as follows...    Pick the willow preset and alter it using these settings.

Branch/Trunk
Distribution 5                                                                                                                                           Branches per segment 1-10
Segments 10-13
Branch start angle 70
Branch end angle 0
Trunk thickness 2-40
Branch thickness 48-50

Tree Shape
Mountain Ash
gravity 100
Randomness 100

Foliage
Weeping Willow
Scale 2
Number of leaves 10                                                                                                                        Distribution Spiral