!ERROR!System:SpeedTreeAssetSpec: no textures specified for <SpeedTree File Name>
To confirm that this is your error you can open the console window and try adding your tree. This error shows no other symptoms.
The problem is probably that you ether have not uploaded your textures for your .spt file or you have not converted them to .dds files. Take a look at Speedtree and make sure you have performed every step there.
If there is a problem even after doing that post in the topic Forums > HeroCloud & HeroEngine > Design & World Building > Add SpeedTrees from library