Sort tree output by PPID

[tklauser]

Otherwise the processes might appear in arbitrary order and
disassociated from their parent process. Also avoid printing a stray
newline after the tree.

Before:

...
├── 2493
│   └── 4952 (gops) {go1.18.1}
├── 1
│   └── 117 (com.docker.vmnetd) {go1.17.5}
├── 4405
│   └── 4416 (gopls) {go1.18.2}
└── 4404

After:

...
├── 1
│   └── 117 (com.docker.vmnetd) {go1.17.5}
├── 2493
│   └── 4945 (gops) {go1.18.3}
└── 4404
    └── 4405 (gopls) {go1.18.2}
        └── 4416 (gopls) {go1.18.2}