Jerry, the adjustment factor to correct for the extra anemometer height can be easily calculated using formulas for wind turbines found here: http://www.motiva.fi/myllarin_tuulivoima/windpower%20web/en/tour/wres/shear.htm
The real trick is estimating an accurate roughness length for those trees. If the surrounding tree heights and densities vary depending on compass direction, then the roughness length will vary somewhat as well for different wind directions. Also if the trees are deciduous, the roughness length will change with the seasons.
I don't if any of the various weather software packages can apply different wind correction factors that are dependent on the wind direction. I've programmed my Meteohub to do so to "increase" my 12' anemometer wind speeds to be equivalent to those at 33 ft (there are several nearby 33 ft wind anemometers to compare with). I need to do the same for my 26' anemometer once I get the time now that I have a half year's worth of data.
Edit: You can get an approximation of the correction necessary by using this calculator at 10m vs. 20m heights: http://www.motiva.fi/myllarin_tuulivoima/windpower%20web/en/tour/wres/calculat.htm