Made in Blender 3.4

Creating Trees with Grease Pencil

Shift+A To add a Grease Pencil Blank object

Make sure that the GPencil object is selected and go to Draw Mode

draw mode is not available when you have other objects selected!

Set strokeplacement to STROKE instead of the default Origin

Type the 1 on the numeric keypad to go Front Orthographic view. When doing so you ensure that the drawing is on a flat - plane.
Draw from the 3D Cursor and make some branches

Shift-Middle-Mouse-Drag To move the view port.
You will see that everyting is on '1 plane' and we don't have other sides

Draw some more with the orientation

Draw a branche each time you rotate the tree

And you might have something like this:

Go to Object mode

Convert the grease pencil object to a path: Object -> Convert -> Path:

Select the GP_Layer.
Go to the Path icon
in Geometry / Bevel change the Depth, Resolution and turn on fill Caps

Go to Edit Mode and select proportional editing

Select some points (click-drag-box)
Press Alt+S and move the mouse to make some parts thicker and some parts thinner.

When you are satisfied with the object : turn it into a mesh :
Go to Object Mode Menu Object
Convert -> Mesh

You can add a material to the mesh to go to the GP_Layer Mesh that is created.
Material Icon (Sphere-ball)
[+] Icon and set the Base Color to brown
For the leafs of the trees we will use a particle system.
See the other tutorials for this