I think it is to bad it is only 40cm long.
Frogs do like to have some space in length as well.
For tree frogs, in my opinion this size is to limited.
Maybe you can use it for a couple of small reedfrogs or something.
Otherwise you can consider putting in one couple of Ranitomeya .
Put in some nice climbing branches, some live plants, bromeliads and leaflitter on the bottom and you will be fine.
R.ventrimaculata would be a great frog to start with in this terrarium.
However, before decorating, descide about the species you like to put in,
this way you can optimize the decoration you put in.