Information

Full output of /ess version:

>ess version
[21:29:36 INFO]: CONSOLE issued server command: /ess version
[21:29:36 INFO]: Server version: 1.11-R0.1-SNAPSHOT git-Spigot-f950f8e-0a81101 (MC: 1.11)
[21:29:36 INFO]: EssentialsX version: 2.15.0.57
[21:29:36 INFO]: PermissionsEx version: 1.23.4
[21:29:36 INFO]: Vault version: 1.5.6-b49
[21:29:36 INFO]: EssentialsXSpawn version: 2.15.0.1
[21:29:36 INFO]: Version mismatch! Please update all Essentials jars to the same version.
>

Server log: Nothing in relation with the issue

EssentialsX config: Tried on a "fresh" server without any config modification

Details

Description
When using /tree or /bigtree the tree won't spawn or spawn on an incorrect location.

Steps to reproduce
Issue 1
-> Place a block of dirt in the void, then, below, 20 or more blocks or air and a block like bedrock or wood (where a tree can't spawn).
-> Point the top block of dirt, and try to spawn a tree

Issue 2
-> Place a block of dirt in the void, then, below, 20 or more blocks or air and a block of dirt (where a tree can spawn).
-> Point the top block of dirt, and try to spawn a tree

Expected behavior
The tree may spawn on the top block of dirt, in the two cases.

Real behavior
1 : The tree doesn't spawn. Error : Big tree generation failure. Try again on grass or dirt.
2 : The tree spawns on the lowest block of dirt.

Picture

In the 3 cases, I used /tree tree command on the top dirt block.
In the third case, it generated an error.

Update : picture added.

Thanks for opening a report and attaching the image, and apologies for the delay in responding to this.

It appears the command looks for the lowest block it can find with the same X and Z coordinates. I'm not sure why this behaviour is the case or if it's intended - we'd need to investigate how this works to figure out what the cause is.