Tree frogs are frogs. They begin as tadpoles swimming around in a body of water. Their eggs aren't laid on plants, but in water. If you have standing water--even in relatively small areas (in gutters, tree stumps, fountains, drainage ditch, etc) tree frogs and other frogs will lay eggs in it and their tadpoles will use it as a nursery.
Your wisteria probably offers shelter for these critters from predators. It's probalby not where the frogs are born and develop though.