Also, I used a "clear" gesso to prepare the surface of the wood. The brand was Liquitex, so I went to their web site and looked at the information to see if they recommended one coat or more. Their site does say that usually only one coat is needed. This clear gesso has some grit in it and helps the paint adhere to it. After starting putting in some of the colors, I could see that the board was "soaking" up the paint. The next time, I will use two coats of the clear gesso.
So . . . Before laying in those upper darks, I did use a Chinese Orange by Sennelier to tone the area that would be underneath those blues and greens. It is a transparent orange, so the grain of the wood is still somewhat visible. Birch panels are relatively light in color, so the grain is not overwhelmingly visible.
Here is a close up of the top of the panel. You can see a little more of the process and the transparent orange used underneath the blues and greens that will start the branches. I always start my greens without green -- usually with a blue, or aqua / turquoise. I do consider painting to be a layering process.
Come back tomorrow and I'll show you the next layer! Ask questions if you wish.