Index: bin/ps/ps.c
===================================================================
--- bin/ps/ps.c
+++ bin/ps/ps.c
@@ -170,7 +170,7 @@
 			"%cpu,%mem,command";
 static char Zfmt[] = "label";
 
-#define	PS_ARGS	"AaCcde" OPT_LAZY_f "G:gHhjJ:LlM:mN:O:o:p:rSTt:U:uvwXxZ"
+#define	PS_ARGS	"AaCcD::de" OPT_LAZY_f "G:gHhjJ:LlM:mN:O:o:p:rSTt:U:uvwXxZ"
 
 int
 main(int argc, char *argv[])
@@ -182,12 +182,13 @@
 	KINFO_STR *ks;
 	struct varent *vent;
 	struct winsize ws = { .ws_row = 0 };
-	const char *nlistf, *memf, *str;
+	const char *nlistf, *memf, *str, *traverse_opts = "";
 	char *cols;
 	int all, ch, elem, flag, _fmt, i, lineno, linelen, left;
 	int descendancy, nentries, nkept, nselectors;
 	int prtheader, wflag, what, xkeep, xkeep_implied;
 	int fwidthmin, fwidthmax;
+	struct { int traversed; int initial; } pid_count;
 	char errbuf[_POSIX2_LINE_MAX];
 	char fmtbuf[_POSIX2_LINE_MAX];
 
@@ -264,6 +265,10 @@
 		case 'c':
 			cflag = 1;
 			break;
+		case 'D':
+			descendancy = 1;
+			traverse_opts = optarg != NULL ? optarg : "$";
+			break;
 		case 'd':
 			descendancy = 1;
 			break;
@@ -504,7 +509,7 @@
 			what = KERN_PROC_PGRP | showthreads;
 			flag = *pgrplist.l.pids;
 			nselectors = 0;
-		} else if (pidlist.count == 1) {
+		} else if (pidlist.count == 1 && traverse_opts[0] == 0) {
 			what = KERN_PROC_PID | showthreads;
 			flag = *pidlist.l.pids;
 			nselectors = 0;
@@ -539,6 +544,33 @@
 	if ((kp == NULL && errno != ESRCH) || (kp != NULL && nentries < 0))
 		xo_errx(1, "%s", kvm_geterr(kd));
 	nkept = 0;
+	pid_count.initial = pidlist.count;
+	if (strchr(traverse_opts, '$') != NULL)
+		for (elem = 0; elem < pidlist.count; elem++)
+			for (i = 0; i < nentries; i++) {
+				if (kp[i].ki_ppid == kp[i].ki_pid)
+					continue;
+				if (kp[i].ki_ppid == pidlist.l.pids[elem]) {
+					if (pidlist.count >= pidlist.maxcount)
+						expand_list(&pidlist);
+					pidlist.l.pids[pidlist.count++] = kp[i].ki_pid;
+				}
+			}
+	pid_count.traversed = pidlist.count;
+	if (strchr(traverse_opts, '^') != NULL)
+		for (elem = 0; elem < pidlist.count; elem++) {
+			if (elem >= pid_count.initial && elem < pid_count.traversed)
+				continue;
+			for (i = 0; i < nentries; i++) {
+				if (kp[i].ki_ppid == kp[i].ki_pid)
+					continue;
+				if (kp[i].ki_pid == pidlist.l.pids[elem]) {
+					if (pidlist.count >= pidlist.maxcount)
+						expand_list(&pidlist);
+					pidlist.l.pids[pidlist.count++] = kp[i].ki_ppid;
+				}
+			}
+		}
 	if (nentries > 0) {
 		if ((kinfo = malloc(nentries * sizeof(*kinfo))) == NULL)
 			xo_errx(1, "malloc failed");