I'm not sure about this but I think all you need is
tree | sed 's/├/\+/g; s/─/-/g; s/└/\\/g'
For example:
$ tree
.
├── file0
└── foo
├── bar
│ └── file2
└── file1
2 directories, 3 files
$ tree | sed 's/├/\+/g; s/─/-/g; s/└/\\/g'
.
+-- file0
\-- foo
+-- bar
│ \-- file2
\-- file1
2 directories, 3 files