Well, it looks solid enough. Though you've put very hard restrictions on it, which makes it feel like it would barely get used. It's more like a secret exit from your lair than the "speed boost", the escape potion can provide. They will work pretty much the same, if you are using them in your lair, but outside, the escape potion is a lot more valuable.
This could probably work simply as an aspect to your lair, a secure way to get out, if you are ever under siege. Pretty much like a mundane secret tunnel, only, well, magic. I really don't think charging any form of item slot for it would be necessary. If you could transform any tree you like into a tunnel to one you've prepared for this, yes, I would have you make it a spell, but this way, I think just describing it as being prepared in your downtime would be enough for me.