src/vs/workbench/contrib/terminal/browser/terminalGroup.ts/SplitPaneContainer/_addChild
class SplitPaneContainer:	private _addChild(instance: ITerminalInstance, index: number): void {
		const child = new SplitPane(instance, this.orientation === Orientation.HORIZONTAL ? this._height : this._width);
		child.orientation = this.orientation;
		if (typeof index === 'number') {
			this._children.splice(index, 0, child);
		} else {
			this._children.push(child);
		}
		this._terminalToPane.set(instance, this._children[this._children.indexOf(child)]);

		this._withDisabledLayout(() => this._splitView.addView(child, Sizing.Distribute, index));
		this.layout(this._width, this._height);

		this._onDidChange = Event.any(...this._children.map(c => c.onDidChange));
	}