Tree Bridge - What do these do?

I've been messing around with the tree bridge doodad in TFT.

What do they do? I can't seem to get anyone to walk on them, what the heck is their purpose?

Maybe when they died, and it was on a perfect position, it becomes a bridge...

That's my logical guess, 'cause if they put it in the BRIDGE section...

press ctrl+page up ctrl+page down to set brisge and door at the right position.
another great exemple is, when you make a stone wall and cant conect them each other..... to conect them hold ctrl and move them whit the arrow on the num. pad.
ctrl have many great utility in the editor....
to set the rotation for a unit hold ctrl and rotate the unit whit the mouse

Yeah you're right. Thanks. This could be useful for something...