Sequencer Slate Widgets - Making a TrackLane Widget for my custom DialogueSequencer

I’m trying to build a UI based on existing and built-in sequencer in UE. The problem is, when i try to create a custom TrackLane this one is not showing up even if i’ve used the same code, maybe scrapping away few details but the idea is the same. Can someone help me to figure out where i can find those instructions used to set the TrackLane’s size to fill horizontally. Thanks.