I think the best way to model these in xlights is by generating a custom model. In xlights, if you click on Tools - Generate Custom Model it will put you in the right direction. Creating your model this way will have xlights draw your model for you via a video capture process. Basically to get started, you need to physically have the model completely built and set up in xlights ( just a single poly line will be fine - you will replace it with the custom model you create later).
You can then run through the Generate Custom Model process in xlights. You take a video of your model while xlights runs a chase sequence on the model. Simply upload the video file to xlights as one of the steps in the Generate Custom Model process. Xlights can then either automatically draw the model for you, or you can manually draw it yourself.
Here is a video Keith made a few years back. Although it was created in 2016, it's still valid and is what I referred to when I created my angel wings model in xlights. View: https://youtu.be/_BBPS1Kyczw
Once you have your model created, you just import the model for every tree you add to your forest. You are welcome to PM me if you get stuck. I literally only did this whole process a few weeks ago myself.