To improve building a mindmap with a keyboard I would suggest to let the escape key delete an empty node and move back up tree if no text has been entered.
Cursor is on Tier 1 node, you press TAB to open an empty Tier 2 and allow for keyboard input
If you press escape at this moment the edit mode will disappear and the cursor will be placed on the Tier 2 node without a label. If you had made a mistake you need to press delete to be taken back to tier 1 and you can make this one keystroke less than it needs to be.
I suggest that the expected behaviour should be something like this
Cursor is on Tier 1, you press tab to open an empty Tier 2 and allow for keyboard input
If you have not added any text and press escape the now empty Tier 2 node would be deleted and the cursor moved back to Tier 1 similar to how the DEL key functions when you delete a node.
This will allow for swift recovery when using Keyboard input to be able to correct mistakes and traverse the tree easily.