Extremely slow with large files

[LGFN]

Running this on a large file (80k lines), takes me 1:35-1:40 minutes to complete. Any way to speed this up (async perhaps)?

Specs:
Processor: Intel(R) Core(TM) i7-3770 CPU @ 3.40GHz, 3401 Mhz, 4 Core(s), 8 Logical Processor(s)
Installed Physical Memory (RAM): 16.0 GB

[triforcely]

Thank you for reporting this problem. I've never tested this extension with a file of this size but I agree that this takes much too long.

I am busy with other things atm, so contributions are more than welcome. We are looking to optimize method in CollapseLevel.cs, line 123.